We present empirical potential and Density Functional Theory results of interstitials in FeCr and... more We present empirical potential and Density Functional Theory results of interstitials in FeCr and pure Cr. Results show that potentials for the original and revised two--band model, a recently introduced third two--band model, and for the revised concentration--dependent model produce errors of up to multiple eV in formation and binding energies for Fe--containing interstitials in pure Cr. Fe--interstitial binding in Cr is much stronger than Cr--interstitial binding in Fe according to Density Functional Theory, but all four potentials still strongly overestimate the binding strength. At the Fe--rich end errors in empirical potentials are smaller and most of the errors are not a linear extrapolation in concentration of the larger errors in pure Cr. Interstitial formation energies in Fe--rich FeCr are underestimated by all four empirical potentials, but much less so than in pure Cr. In Fe--rich FeCr the revised concentration--dependent model produces Cr--interstitial binding energies quite similar to Density Functional Theory values, while all three two--band models show almost no binding or repulsion. 1 Introduction FeCr is an alloy that has good properties for application as a structural material in nuclear environments. Since operating conditions like MeV neutron bombardment coming from fusion plasma can only be studied in special facilities, the alloy has been the subject of extensive atomistic modelling for over a decade. Much of the atomistic simulation work has come in the form of molecular dynamics or atomistic Monte Carlo simulations employing empirical potentials. Several FeCr potentials have been constructed explicitly in the context of radiation damage, including reproducing the change of sign in the heat of formation in Fe--rich FeCr, i.e. the original [1, 2] and revised [3] versions of the two--band model (2BM) and the revised [4] version of the concentration dependent model (CDM). These potentials represent the established state of the art for atomistic radiation damage modelling of FeCr systems too large to be handled by electronic structure methods, like Density Functional Theory (DFT). Recently, Eich et al [5] published a third 2BM potential, focussing on an accurate thermodynamic description at both low and high temperature. During the construction of the original and revised 2BM and CDM, attention was focussed mostly on the Fe--rich end of the concentration range, since structural FeCr alloys consist mostly of Fe. Fitting data included Cr atoms interacting with or becoming part of self--interstitials, the archetypal point defect found in metals only after exposure to radiation. By contrast, the 3 rd 2BM by Eich et al did not include point defect data in the fitting. Despite the application of the original and revised 2BM potentials and the CDM potential in many studies (on topics including phase diagram prediction [e.g. 6, 7], phase separation, [e.g. 8], homogeneous [e.g. 9] and heterogeneous [e.g. 10] precipitation, short [e.g. 11, 12] and long range order [e.g. 13], impact cascades [e.g. 14--16], microstructure [e.g. 17--19], Cr--interstitial interaction [e.g. 20, 21], Cr--dislocation interaction [e.g. 22--24], dislocation--precipitate interaction [e.g. 25], grain boundary segregation [e.g. 26, 27], radiation--induced segregation [e.g. 28], point defect annealing [e.g. 29], effect of Cr concentration on vacancy stability [e.g. 4],vacancy cluster stability [e.g. 30], bubble formation [e.g. 31]) and their detailed benchmarking [32--35] to assess their strengths and weaknesses, it is still not fully known which situations they manage or fail to describe accurately. The 3 rd 2BM by Eich et al has not been as extensively tested yet since its publication in 2015. Recently, we calculated interstitial formation energies with the revised CDM in FeCr alloys with 1--17 atom% Cr and found an unlikely formation energy trend that decreased with increasing Cr concentration, see below. This prompted us to investigate how accurate FeCr interstitial formation energies are reproduced at the Cr--rich end and if the energies might be 'extrapolating towards the wrong end value' in pure Cr. Having established, by comparing empirical potential and DFT results, that this is indeed the case, we determined how much of the large errors present in pure Cr are still present at concentrations in the Fe--rich end. The build--up of this paper is as follows. In the next section a description of the computational methodology is presented. In section 3.1 CDM results are presented for interstitials in 1--17 atom% Cr, showing the aforementioned questionable formation energy trend in that concentration range. In section 3.2 we compare revised CDM and original, revised, and 3rd 2BM results for FeFe and FeCr interstitials (and Fe solutes next to vacancies) in pure Cr to DFT, showing that all four of these empirical potentials produce big errors for Fe--containing interstitials in pure Cr. Then in section 3.3 we show how much of the errors for pure Cr are still present at two Cr concentrations (8 and 16%) in the Fe--rich end. Finally, in latter part of the summary and conclusions section we briefly discuss how to improve the empirical potentials. 2 Computational details Empirical potential calculations were performed with four different potentials obtained following two different extensions to the EAM formalism: a CDM model , modified to better describe the relative energy of the mixed interstitials [4]; the original [1, 2] 2BM model; the revised 2BM [3], modified to better describe
Journal of the Chemical Society Chemical Communications
Page 1. H H H E H H E H H H H H E H H HH H E H side-on, Cs D3h C Si, Ge Cs The role of back-bondi... more Page 1. H H H E H H E H H H H H E H H HH H E H side-on, Cs D3h C Si, Ge Cs The role of back-bonding in the determination of classical vs. non-classical bonding in EH3 + and EH5 + minimum structures for E = C, Si and Ge ...
The reaction of propargyl cation with water was investigated at the CCSD(T)/6-311+G(2df,2p)//MP2-... more The reaction of propargyl cation with water was investigated at the CCSD(T)/6-311+G(2df,2p)//MP2-FULL/6-31+G(d,p) theory level by performing a statistical thermodynamics analysis of the theoretical results. We located five endothermic reaction channels, H2CCC+H3O+ and four c-C3H2+H3O+ by 47.8 and 35.7kcal/mol in Gibbs energy, respectively, and eight exothermic reaction channels, four c-C3H3++H2O (−26.5kcal/mol), two C3H3O++H2O (−43.4kcal/mol), and two C3H3·OH2+ (−56.0kcal/mol). The rate determining
An ab initio study of the s attack of CH 2 F 1 on acetylene at the MP4(SDTQ)-FC/6-31G pp //MP2-FC... more An ab initio study of the s attack of CH 2 F 1 on acetylene at the MP4(SDTQ)-FC/6-31G pp //MP2-FC/6-31G pp 1ZPVE (MP2) level was performed. According to our results there are one reaction channel leading to C 3 H 3 1 1HF and three reaction channels rendering C 3 H 2 F 1 1H 2. The statistical production of C 3 H 3 1 obtained through these s channels, that require a practically collinear collision of the reactants, and the p channel previously reported allows to explain the relatively low yield of C 3 H 3 1 experimentally observed.
ABSTRACT An MP4(full,SDTQ)/6-311++G(d,p)//MP2(full)/6-311++G(d,p) ab initio study was performed o... more ABSTRACT An MP4(full,SDTQ)/6-311++G(d,p)//MP2(full)/6-311++G(d,p) ab initio study was performed of the reactions of formyl and isoformyl cations with H2O and NH3, which play an important role in flame and interstellar chemistries. Two different confluent channels were located leading to CO+H3O+/NH. The first one corresponds to the approach of the neutral molecule to the carbon atom of the cations. The second one leads to the direct proton transfer from the cations to the neutrals. At 900 K the separate products CO+H3O+/NH are the most stable species along the Gibbs energy profiles for the processes. For the reaction with H2O the reaction channel leading to HC(OH) (protonated formic acid) is disfavored with respect to the two CO+H3O+ channels in agreement with the experimental evidence that H3O+ is the major ion observed in hydrocarbon flames. According to our calculations, NH+H2O are considerably more stable in Gibbs energy than NH3+H3O+;NH will predominate in the reaction zone when ammonia is added to CH4+Ar diffusion flame, as experimentally observed. At 100 K the most stable structures are the intermediate complexes CO…HOH/HNH. Particularly the CO…HOH complex has a lifetime large enough to be detected and, therefore, could play a certain role in interstellar chemistry.
Diode-Pumped High Energy and High Power Lasers; ELI: Ultrarelativistic Laser-Matter Interactions and Petawatt Photonics; and HiPER: the European Pathway to Laser Energy, 2011
HiPER is the European Project for Laser Fusion that has been able to join 26 institutions and sig... more HiPER is the European Project for Laser Fusion that has been able to join 26 institutions and signed under formal government agreement by 6 countries inside the ESFRI Program of the European Union (EU). The project is already extended by EU for two years more (until 2013) after its first preparatory phase from 2008. A large work has been developed
We present empirical potential and Density Functional Theory results of interstitials in FeCr and... more We present empirical potential and Density Functional Theory results of interstitials in FeCr and pure Cr. Results show that potentials for the original and revised two-‐band model, a recently introduced third two-‐band model, and for the revised concentration-‐dependent model produce errors of up to multiple eV in formation and binding energies for Fe-‐containing interstitials in pure Cr. Fe-‐interstitial binding in Cr is much stronger than Cr-‐interstitial binding in Fe according to Density Functional Theory, but all four potentials still strongly overestimate the binding strength. At the Fe-‐rich end errors in empirical potentials are smaller and most of the errors are not a linear extrapolation in concentration of the larger errors in pure Cr. Interstitial formation energies in Fe-‐rich FeCr are underestimated by all four empirical potentials, but much less so than in pure Cr. In Fe-‐rich FeCr the revised concentration-‐dependent model produces Cr-‐interstitial binding energies quite similar to Density Functional Theory values, while all three two-‐band models show almost no binding or repulsion.
This work aims at identifying common potential problems that future fusion devices will encounter... more This work aims at identifying common potential problems that future fusion devices will encounter for both magnetic (MC) and inertial (IC) confinement approaches in order to promote joint efforts and to avoid duplication of research.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
... E2 and S N 2 Reactions of X − + CH 3 CH 2 Cl (X = F, Cl, Br, HO, HS, HSe ... Xiao-Peng Wu, Xi... more ... E2 and S N 2 Reactions of X − + CH 3 CH 2 Cl (X = F, Cl, Br, HO, HS, HSe ... Xiao-Peng Wu, Xiao-Ming Sun, Xi-Guang Wei, Yi Ren, Ning-Bew Wong and Wai-Kee Li. ... Pablo Campomanes, Dimas Suárez, and Tomás L. Sordo. The Journal of Physical Chemistry A 1999 103 (30), 5996 ...
An ab initio study of the (PC3H)+ and (PC3H2)+ species was carried out. Since the ionization pote... more An ab initio study of the (PC3H)+ and (PC3H2)+ species was carried out. Since the ionization potential of C-C3H2 is lower than that of phosphorus, the reaction in the interstellar medium is more likely to be initiated by P+c-C3H2+. In that case, only production of a four-membered ring PC3H+ species should be feasible. The reactions of P with c-C3H2+ and of P+ with 1-C3H2 are feasible in the interstellar medium and consequently possible sources of precursors of C3P in space.
Nuclear Instruments and Methods in Physics Research, 2013
ABSTRACT Fe–Cr based alloys are the leading structural material candidates in the design of next ... more ABSTRACT Fe–Cr based alloys are the leading structural material candidates in the design of next generation reactors due to their high resistance to swelling and corrosion. Despite these good properties there are others, such as embrittlement, which require a higher level of understanding in order to improve aspects such as safety or lifetime of the reactors. The addition of Cr improves the behavior of the steels under irradiation, but not in a monotonic way. Therefore, understanding the changes in the Fe–Cr based alloys microstructure induced by irradiation and the role played by the alloying element (Cr) is needed in order to predict the response of these materials under the extreme conditions they are going to support. In this work we perform a study of the effect of Cr concentration in a bcc Fe–Cr matrix on formation and binding energies of vacancy clusters up to 5 units. The dependence of the calculated formation and binding energy is investigated with two empirical interatomic potentials specially developed to study radiation damage in Fe–Cr alloys. Results are very similar for both potentials showing an increase of the defect stability with the cluster size and no real dependence on Cr concentration for the binding energy
C 6 H 7 + has been investigated by using the ab initio method at MP2-FC/6-31G* level and single p... more C 6 H 7 + has been investigated by using the ab initio method at MP2-FC/6-31G* level and single point calculations on the MP2 geometries at the MP4(SDTQ)-FC/6-31G* level. The most stable structure located corresponds to the benzenium ion C 6 H 7 + in which a proton is bonded to one of the carbon atoms of the benzene ring and an extension of the delocalization has taken place to include the attached proton, the π-electron density distribution being basically allylic in agreement with experimental findings. Two transition structures (TSs) for hydrogen scrambling were found on the C 6 H 7 + PES. The first one corresponds to the peripheral migration of a proton in the benzenium ion and determines an energy barrier of 7.8 kcal/mol at MP2 level (10.8 at MP4//MP2 level) in good agreement with experimental data. The second scrambling TS corresponds to the interchange of the two hydrogen atoms bonded to the same carbon atom in the ring of the benzenium ion and presents an energy barrier of 59.2 kcal/mol at MP2 level (62.6 at MP4//MP2 level). The H 2 -elimination is an endoergic process that proceeds through a very late TS and an intermediate very close in energy to it that finally renders the products, C 6 H 5 + + H 2 , without any energy barrier. The activation energy for this process (70.3 and 70.1 kcal/mol at MP2 and MP4//MP2 levels, respectively) is practically its endoergicity (71.1 kcal/mol at MP2 level and 70.8 kcal/mol at MP4//MP2 level) in accordance with the experimental finding of null energy release as relative motion between the fragments. A configuration analysis of the wave function of C 6 H 7 + along the reaction coordinate for H 2 -elimination clearly shows that the back-donation from the NHOMO of C 6 H 5 + to the LUMO of H 2 plays a fundamental role in the bonding structure of the benzenium ion. The H 2 elimination takes place through deactivation of the back-bonding at an early stage in the process.
ABSTRACT An account of the first theoretical studies on the role of back-bonding in carbocation c... more ABSTRACT An account of the first theoretical studies on the role of back-bonding in carbocation chemistry is presented. The bonding structure of EH3+ and EH5+ (E=C, Si, Ge) species may be rationalised by means of a back-bonding interaction between EH+ and EH3+ moieties and H2. Back-bonding interaction between C6H5+ and H2 is also crucial for the formation of the benzenium ion, C6H7+. Back-donation determines the H2 elimination channels from benzenium ion and ethyl cation as well. In effect, the hydrogen molecule can be eliminated only when the two C-H bonds involved stretch and the back-bonding is weak. In the case of ethyl cation this condition implies that the simultaneous stretching of the two C-H bonds takes place out of phase with the C-C elongation. Thus, the concept of back-donation, which plays a fundamental role in explaining the bonding between certain ligands and transition metal atoms, between certain nonmetals, and the bonding structure of π and σ complexes is also essential for understanding carbocation chemistry.
Theoretical Studies of the Formation of β-Lactams -[51 refs.]. -(LOPEZ, R.; DEL RIO, E.; DIAZ, N.... more Theoretical Studies of the Formation of β-Lactams -[51 refs.]. -(LOPEZ, R.; DEL RIO, E.; DIAZ, N.; SUAREZ, D.; MENENDEZ, M. I.; SORDO, T. L.; Recent Res. Dev.
ABSTRACT An account of the first theoretical studies on the role of back-bonding in carbocation c... more ABSTRACT An account of the first theoretical studies on the role of back-bonding in carbocation chemistry is presented. The bonding structure of EH3+ and EH5+ (E=C, Si, Ge) species may be rationalised by means of a back-bonding interaction between EH+ and EH3+ moieties and H2. Back-bonding interaction between C6H5+ and H2 is also crucial for the formation of the benzenium ion, C6H7+. Back-donation determines the H2 elimination channels from benzenium ion and ethyl cation as well. In effect, the hydrogen molecule can be eliminated only when the two C-H bonds involved stretch and the back-bonding is weak. In the case of ethyl cation this condition implies that the simultaneous stretching of the two C-H bonds takes place out of phase with the C-C elongation. Thus, the concept of back-donation, which plays a fundamental role in explaining the bonding between certain ligands and transition metal atoms, between certain nonmetals, and the bonding structure of π and σ complexes is also essential for understanding carbocation chemistry.
An ab initio molecular orbital study has been carried out for the C 3 P radical and its positive ... more An ab initio molecular orbital study has been carried out for the C 3 P radical and its positive ion, C 3 P + . Geometries, vibrational frequencies, and infrared intensities have been obtained at the MP2/6-31G* level, whereas MP4 theory has been employed to compute electronic ...
We present empirical potential and Density Functional Theory results of interstitials in FeCr and... more We present empirical potential and Density Functional Theory results of interstitials in FeCr and pure Cr. Results show that potentials for the original and revised two--band model, a recently introduced third two--band model, and for the revised concentration--dependent model produce errors of up to multiple eV in formation and binding energies for Fe--containing interstitials in pure Cr. Fe--interstitial binding in Cr is much stronger than Cr--interstitial binding in Fe according to Density Functional Theory, but all four potentials still strongly overestimate the binding strength. At the Fe--rich end errors in empirical potentials are smaller and most of the errors are not a linear extrapolation in concentration of the larger errors in pure Cr. Interstitial formation energies in Fe--rich FeCr are underestimated by all four empirical potentials, but much less so than in pure Cr. In Fe--rich FeCr the revised concentration--dependent model produces Cr--interstitial binding energies quite similar to Density Functional Theory values, while all three two--band models show almost no binding or repulsion. 1 Introduction FeCr is an alloy that has good properties for application as a structural material in nuclear environments. Since operating conditions like MeV neutron bombardment coming from fusion plasma can only be studied in special facilities, the alloy has been the subject of extensive atomistic modelling for over a decade. Much of the atomistic simulation work has come in the form of molecular dynamics or atomistic Monte Carlo simulations employing empirical potentials. Several FeCr potentials have been constructed explicitly in the context of radiation damage, including reproducing the change of sign in the heat of formation in Fe--rich FeCr, i.e. the original [1, 2] and revised [3] versions of the two--band model (2BM) and the revised [4] version of the concentration dependent model (CDM). These potentials represent the established state of the art for atomistic radiation damage modelling of FeCr systems too large to be handled by electronic structure methods, like Density Functional Theory (DFT). Recently, Eich et al [5] published a third 2BM potential, focussing on an accurate thermodynamic description at both low and high temperature. During the construction of the original and revised 2BM and CDM, attention was focussed mostly on the Fe--rich end of the concentration range, since structural FeCr alloys consist mostly of Fe. Fitting data included Cr atoms interacting with or becoming part of self--interstitials, the archetypal point defect found in metals only after exposure to radiation. By contrast, the 3 rd 2BM by Eich et al did not include point defect data in the fitting. Despite the application of the original and revised 2BM potentials and the CDM potential in many studies (on topics including phase diagram prediction [e.g. 6, 7], phase separation, [e.g. 8], homogeneous [e.g. 9] and heterogeneous [e.g. 10] precipitation, short [e.g. 11, 12] and long range order [e.g. 13], impact cascades [e.g. 14--16], microstructure [e.g. 17--19], Cr--interstitial interaction [e.g. 20, 21], Cr--dislocation interaction [e.g. 22--24], dislocation--precipitate interaction [e.g. 25], grain boundary segregation [e.g. 26, 27], radiation--induced segregation [e.g. 28], point defect annealing [e.g. 29], effect of Cr concentration on vacancy stability [e.g. 4],vacancy cluster stability [e.g. 30], bubble formation [e.g. 31]) and their detailed benchmarking [32--35] to assess their strengths and weaknesses, it is still not fully known which situations they manage or fail to describe accurately. The 3 rd 2BM by Eich et al has not been as extensively tested yet since its publication in 2015. Recently, we calculated interstitial formation energies with the revised CDM in FeCr alloys with 1--17 atom% Cr and found an unlikely formation energy trend that decreased with increasing Cr concentration, see below. This prompted us to investigate how accurate FeCr interstitial formation energies are reproduced at the Cr--rich end and if the energies might be 'extrapolating towards the wrong end value' in pure Cr. Having established, by comparing empirical potential and DFT results, that this is indeed the case, we determined how much of the large errors present in pure Cr are still present at concentrations in the Fe--rich end. The build--up of this paper is as follows. In the next section a description of the computational methodology is presented. In section 3.1 CDM results are presented for interstitials in 1--17 atom% Cr, showing the aforementioned questionable formation energy trend in that concentration range. In section 3.2 we compare revised CDM and original, revised, and 3rd 2BM results for FeFe and FeCr interstitials (and Fe solutes next to vacancies) in pure Cr to DFT, showing that all four of these empirical potentials produce big errors for Fe--containing interstitials in pure Cr. Then in section 3.3 we show how much of the errors for pure Cr are still present at two Cr concentrations (8 and 16%) in the Fe--rich end. Finally, in latter part of the summary and conclusions section we briefly discuss how to improve the empirical potentials. 2 Computational details Empirical potential calculations were performed with four different potentials obtained following two different extensions to the EAM formalism: a CDM model , modified to better describe the relative energy of the mixed interstitials [4]; the original [1, 2] 2BM model; the revised 2BM [3], modified to better describe
Journal of the Chemical Society Chemical Communications
Page 1. H H H E H H E H H H H H E H H HH H E H side-on, Cs D3h C Si, Ge Cs The role of back-bondi... more Page 1. H H H E H H E H H H H H E H H HH H E H side-on, Cs D3h C Si, Ge Cs The role of back-bonding in the determination of classical vs. non-classical bonding in EH3 + and EH5 + minimum structures for E = C, Si and Ge ...
The reaction of propargyl cation with water was investigated at the CCSD(T)/6-311+G(2df,2p)//MP2-... more The reaction of propargyl cation with water was investigated at the CCSD(T)/6-311+G(2df,2p)//MP2-FULL/6-31+G(d,p) theory level by performing a statistical thermodynamics analysis of the theoretical results. We located five endothermic reaction channels, H2CCC+H3O+ and four c-C3H2+H3O+ by 47.8 and 35.7kcal/mol in Gibbs energy, respectively, and eight exothermic reaction channels, four c-C3H3++H2O (−26.5kcal/mol), two C3H3O++H2O (−43.4kcal/mol), and two C3H3·OH2+ (−56.0kcal/mol). The rate determining
An ab initio study of the s attack of CH 2 F 1 on acetylene at the MP4(SDTQ)-FC/6-31G pp //MP2-FC... more An ab initio study of the s attack of CH 2 F 1 on acetylene at the MP4(SDTQ)-FC/6-31G pp //MP2-FC/6-31G pp 1ZPVE (MP2) level was performed. According to our results there are one reaction channel leading to C 3 H 3 1 1HF and three reaction channels rendering C 3 H 2 F 1 1H 2. The statistical production of C 3 H 3 1 obtained through these s channels, that require a practically collinear collision of the reactants, and the p channel previously reported allows to explain the relatively low yield of C 3 H 3 1 experimentally observed.
ABSTRACT An MP4(full,SDTQ)/6-311++G(d,p)//MP2(full)/6-311++G(d,p) ab initio study was performed o... more ABSTRACT An MP4(full,SDTQ)/6-311++G(d,p)//MP2(full)/6-311++G(d,p) ab initio study was performed of the reactions of formyl and isoformyl cations with H2O and NH3, which play an important role in flame and interstellar chemistries. Two different confluent channels were located leading to CO+H3O+/NH. The first one corresponds to the approach of the neutral molecule to the carbon atom of the cations. The second one leads to the direct proton transfer from the cations to the neutrals. At 900 K the separate products CO+H3O+/NH are the most stable species along the Gibbs energy profiles for the processes. For the reaction with H2O the reaction channel leading to HC(OH) (protonated formic acid) is disfavored with respect to the two CO+H3O+ channels in agreement with the experimental evidence that H3O+ is the major ion observed in hydrocarbon flames. According to our calculations, NH+H2O are considerably more stable in Gibbs energy than NH3+H3O+;NH will predominate in the reaction zone when ammonia is added to CH4+Ar diffusion flame, as experimentally observed. At 100 K the most stable structures are the intermediate complexes CO…HOH/HNH. Particularly the CO…HOH complex has a lifetime large enough to be detected and, therefore, could play a certain role in interstellar chemistry.
Diode-Pumped High Energy and High Power Lasers; ELI: Ultrarelativistic Laser-Matter Interactions and Petawatt Photonics; and HiPER: the European Pathway to Laser Energy, 2011
HiPER is the European Project for Laser Fusion that has been able to join 26 institutions and sig... more HiPER is the European Project for Laser Fusion that has been able to join 26 institutions and signed under formal government agreement by 6 countries inside the ESFRI Program of the European Union (EU). The project is already extended by EU for two years more (until 2013) after its first preparatory phase from 2008. A large work has been developed
We present empirical potential and Density Functional Theory results of interstitials in FeCr and... more We present empirical potential and Density Functional Theory results of interstitials in FeCr and pure Cr. Results show that potentials for the original and revised two-‐band model, a recently introduced third two-‐band model, and for the revised concentration-‐dependent model produce errors of up to multiple eV in formation and binding energies for Fe-‐containing interstitials in pure Cr. Fe-‐interstitial binding in Cr is much stronger than Cr-‐interstitial binding in Fe according to Density Functional Theory, but all four potentials still strongly overestimate the binding strength. At the Fe-‐rich end errors in empirical potentials are smaller and most of the errors are not a linear extrapolation in concentration of the larger errors in pure Cr. Interstitial formation energies in Fe-‐rich FeCr are underestimated by all four empirical potentials, but much less so than in pure Cr. In Fe-‐rich FeCr the revised concentration-‐dependent model produces Cr-‐interstitial binding energies quite similar to Density Functional Theory values, while all three two-‐band models show almost no binding or repulsion.
This work aims at identifying common potential problems that future fusion devices will encounter... more This work aims at identifying common potential problems that future fusion devices will encounter for both magnetic (MC) and inertial (IC) confinement approaches in order to promote joint efforts and to avoid duplication of research.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
... E2 and S N 2 Reactions of X − + CH 3 CH 2 Cl (X = F, Cl, Br, HO, HS, HSe ... Xiao-Peng Wu, Xi... more ... E2 and S N 2 Reactions of X − + CH 3 CH 2 Cl (X = F, Cl, Br, HO, HS, HSe ... Xiao-Peng Wu, Xiao-Ming Sun, Xi-Guang Wei, Yi Ren, Ning-Bew Wong and Wai-Kee Li. ... Pablo Campomanes, Dimas Suárez, and Tomás L. Sordo. The Journal of Physical Chemistry A 1999 103 (30), 5996 ...
An ab initio study of the (PC3H)+ and (PC3H2)+ species was carried out. Since the ionization pote... more An ab initio study of the (PC3H)+ and (PC3H2)+ species was carried out. Since the ionization potential of C-C3H2 is lower than that of phosphorus, the reaction in the interstellar medium is more likely to be initiated by P+c-C3H2+. In that case, only production of a four-membered ring PC3H+ species should be feasible. The reactions of P with c-C3H2+ and of P+ with 1-C3H2 are feasible in the interstellar medium and consequently possible sources of precursors of C3P in space.
Nuclear Instruments and Methods in Physics Research, 2013
ABSTRACT Fe–Cr based alloys are the leading structural material candidates in the design of next ... more ABSTRACT Fe–Cr based alloys are the leading structural material candidates in the design of next generation reactors due to their high resistance to swelling and corrosion. Despite these good properties there are others, such as embrittlement, which require a higher level of understanding in order to improve aspects such as safety or lifetime of the reactors. The addition of Cr improves the behavior of the steels under irradiation, but not in a monotonic way. Therefore, understanding the changes in the Fe–Cr based alloys microstructure induced by irradiation and the role played by the alloying element (Cr) is needed in order to predict the response of these materials under the extreme conditions they are going to support. In this work we perform a study of the effect of Cr concentration in a bcc Fe–Cr matrix on formation and binding energies of vacancy clusters up to 5 units. The dependence of the calculated formation and binding energy is investigated with two empirical interatomic potentials specially developed to study radiation damage in Fe–Cr alloys. Results are very similar for both potentials showing an increase of the defect stability with the cluster size and no real dependence on Cr concentration for the binding energy
C 6 H 7 + has been investigated by using the ab initio method at MP2-FC/6-31G* level and single p... more C 6 H 7 + has been investigated by using the ab initio method at MP2-FC/6-31G* level and single point calculations on the MP2 geometries at the MP4(SDTQ)-FC/6-31G* level. The most stable structure located corresponds to the benzenium ion C 6 H 7 + in which a proton is bonded to one of the carbon atoms of the benzene ring and an extension of the delocalization has taken place to include the attached proton, the π-electron density distribution being basically allylic in agreement with experimental findings. Two transition structures (TSs) for hydrogen scrambling were found on the C 6 H 7 + PES. The first one corresponds to the peripheral migration of a proton in the benzenium ion and determines an energy barrier of 7.8 kcal/mol at MP2 level (10.8 at MP4//MP2 level) in good agreement with experimental data. The second scrambling TS corresponds to the interchange of the two hydrogen atoms bonded to the same carbon atom in the ring of the benzenium ion and presents an energy barrier of 59.2 kcal/mol at MP2 level (62.6 at MP4//MP2 level). The H 2 -elimination is an endoergic process that proceeds through a very late TS and an intermediate very close in energy to it that finally renders the products, C 6 H 5 + + H 2 , without any energy barrier. The activation energy for this process (70.3 and 70.1 kcal/mol at MP2 and MP4//MP2 levels, respectively) is practically its endoergicity (71.1 kcal/mol at MP2 level and 70.8 kcal/mol at MP4//MP2 level) in accordance with the experimental finding of null energy release as relative motion between the fragments. A configuration analysis of the wave function of C 6 H 7 + along the reaction coordinate for H 2 -elimination clearly shows that the back-donation from the NHOMO of C 6 H 5 + to the LUMO of H 2 plays a fundamental role in the bonding structure of the benzenium ion. The H 2 elimination takes place through deactivation of the back-bonding at an early stage in the process.
ABSTRACT An account of the first theoretical studies on the role of back-bonding in carbocation c... more ABSTRACT An account of the first theoretical studies on the role of back-bonding in carbocation chemistry is presented. The bonding structure of EH3+ and EH5+ (E=C, Si, Ge) species may be rationalised by means of a back-bonding interaction between EH+ and EH3+ moieties and H2. Back-bonding interaction between C6H5+ and H2 is also crucial for the formation of the benzenium ion, C6H7+. Back-donation determines the H2 elimination channels from benzenium ion and ethyl cation as well. In effect, the hydrogen molecule can be eliminated only when the two C-H bonds involved stretch and the back-bonding is weak. In the case of ethyl cation this condition implies that the simultaneous stretching of the two C-H bonds takes place out of phase with the C-C elongation. Thus, the concept of back-donation, which plays a fundamental role in explaining the bonding between certain ligands and transition metal atoms, between certain nonmetals, and the bonding structure of π and σ complexes is also essential for understanding carbocation chemistry.
Theoretical Studies of the Formation of β-Lactams -[51 refs.]. -(LOPEZ, R.; DEL RIO, E.; DIAZ, N.... more Theoretical Studies of the Formation of β-Lactams -[51 refs.]. -(LOPEZ, R.; DEL RIO, E.; DIAZ, N.; SUAREZ, D.; MENENDEZ, M. I.; SORDO, T. L.; Recent Res. Dev.
ABSTRACT An account of the first theoretical studies on the role of back-bonding in carbocation c... more ABSTRACT An account of the first theoretical studies on the role of back-bonding in carbocation chemistry is presented. The bonding structure of EH3+ and EH5+ (E=C, Si, Ge) species may be rationalised by means of a back-bonding interaction between EH+ and EH3+ moieties and H2. Back-bonding interaction between C6H5+ and H2 is also crucial for the formation of the benzenium ion, C6H7+. Back-donation determines the H2 elimination channels from benzenium ion and ethyl cation as well. In effect, the hydrogen molecule can be eliminated only when the two C-H bonds involved stretch and the back-bonding is weak. In the case of ethyl cation this condition implies that the simultaneous stretching of the two C-H bonds takes place out of phase with the C-C elongation. Thus, the concept of back-donation, which plays a fundamental role in explaining the bonding between certain ligands and transition metal atoms, between certain nonmetals, and the bonding structure of π and σ complexes is also essential for understanding carbocation chemistry.
An ab initio molecular orbital study has been carried out for the C 3 P radical and its positive ... more An ab initio molecular orbital study has been carried out for the C 3 P radical and its positive ion, C 3 P + . Geometries, vibrational frequencies, and infrared intensities have been obtained at the MP2/6-31G* level, whereas MP4 theory has been employed to compute electronic ...
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