Papers by Mutasem Sinnokrot
Chemistry-a European Journal, 2006
Journal of The American Chemical Society, 2002
State-of-the-art electronic structure methods have been applied to the simplest prototype of arom... more State-of-the-art electronic structure methods have been applied to the simplest prototype of aromatic π−π interactions, the benzene dimer. By comparison to results with a large aug-cc-pVTZ basis set, we demonstrate that more modest basis sets such as aug-cc-pVDZ are sufficient for ...
Journal of Computational Chemistry, 2009
Several popular force fields, namely, CHARMM, AMBER, OPLS-AA, and MM3, have been tested for their... more Several popular force fields, namely, CHARMM, AMBER, OPLS-AA, and MM3, have been tested for their ability to reproduce highly accurate quantum mechanical potential energy curves for noncovalent interactions in the benzene dimer, the benzene-CH 4 complex, and the benzene-H 2 S complex. All of the force fields are semi-quantitatively correct, but none of them is consistently reliable quantitatively. Re-optimization of Lennard-Jones parameters and symmetry-adapted perturbation theory analysis for the benzene dimer suggests that better agreement cannot be expected unless more flexible functional forms (particularly for the electrostatic contributions) are employed for the empirical force fields.
Journal of Physical Chemistry A, 2006
Noncovalent C-H/π interactions are prevalent in biochemistry and are important in molecular recog... more Noncovalent C-H/π interactions are prevalent in biochemistry and are important in molecular recognition. In this work, we present potential energy curves for methane-benzene, methane-phenol, and methaneindole complexes as prototypes for interactions between C-H bonds and the aromatic components of phenylalanine, tyrosine, and tryptophan. Second-order perturbation theory (MP2) is used in conjunction with the aug-cc-pVDZ and aug-cc-pVTZ basis sets to determine the counterpoise-corrected interaction energy for selected complex configurations. Using corrections for higher-order electron correlation determined with coupled-cluster theory through perturbative triples [CCSD(T)] in the aug-cc-pVDZ basis set, we estimate, through an additive approximation, results at the very accurate CCSD(T)/aug-cc-pVTZ level of theory. Symmetry-adapted perturbation theory (SAPT) is employed to determine the physically significant components of the total interaction energy for each complex.
Journal of Physical Chemistry A, 2003
State-of-the-art electronic structure methods have been applied to obtain the first high-quality ... more State-of-the-art electronic structure methods have been applied to obtain the first high-quality theoretical results for substituent effects in π-stacking interactions. The sandwich configurations of benzene dimer, benzene-phenol, benzene-toluene, benzene-fluorobenzene, and benzene-benzonitrile have been studied using correlation consistent basis sets augmented by multiple diffuse functions, namely aug-cc-pVDZ and aug-cc-pVTZ, at the second-order perturbation theory (MP2) level. Coupled-cluster computations with perturbative triples [CCSD(T)] were performed and combined with the above MP2 calculations to estimate the CCSD(T)/aug-cc-pVTZ binding energies, which should be accurate within several tenths of a kcal mol -1 . All substituted dimers bind more strongly than benzene dimer, with benzene-benzonitrile binding the most strongly. Both electrostatic and dispersion interactions contribute to the increased binding of the monosubstituted dimers.
Journal of The American Chemical Society, 2004
Sandwich and T-shaped configurations of benzene dimer, benzene-phenol, benzene-toluene, benzene-f... more Sandwich and T-shaped configurations of benzene dimer, benzene-phenol, benzene-toluene, benzene-fluorobenzene, and benzene-benzonitrile are studied by coupled-cluster theory to elucidate how substituents tune π-π interactions. All substituted sandwich dimers bind more strongly than benzene dimer, whereas the T-shaped configurations bind more or less favorably depending on the substituent. Symmetryadapted perturbation theory (SAPT) indicates that electrostatic, dispersion, induction, and exchange-repulsion contributions are all significant to the overall binding energies, and all but induction are important in determining relative energies. Models of π-π interactions based solely on electrostatics, such as the Hunter-Sanders rules, do not seem capable of explaining the energetic ordering of the dimers considered.
Chemical Physics, 2001
The reliability of density functional theory and other electronic structure methods is examined f... more The reliability of density functional theory and other electronic structure methods is examined for anharmonicities and spectroscopic constants of the ground electronic states of several diatomic molecules. The equilibrium bond length re, harmonic vibrational frequency ωe, vibrational anharmonicity ωexe, rotational constant Be, centrifugal distortion constant De, and vibration-rotation interaction constant αe have been obtained theoretically for BF, CO, N2, CH+, and H2. Predictions using Hartree-Fock, coupled-cluster singles and doubles (CCSD), coupled cluster singles and doubles with perturbative triples [CCSD(T)], and various density functional methods (S-VWN, BLYP, and B3LYP) have been made using the 6-31G*, aug-cc-pVDZ, and aug-cc-pVTZ basis sets and compared to experimental values. Density functional theory predictions of the spectroscopic constants are reliable (particularly for B3LYP) and often perform as well as the more expensive CCSD and CCSD(T) estimates.
Journal of Computational Chemistry, 2009
Several popular force fields, namely, CHARMM, AMBER, OPLS-AA, and MM3, have been tested for their... more Several popular force fields, namely, CHARMM, AMBER, OPLS-AA, and MM3, have been tested for their ability to reproduce highly accurate quantum mechanical potential energy curves for noncovalent interactions in the benzene dimer, the benzene-CH 4 complex, and the benzene-H 2 S complex. All of the force fields are semi-quantitatively correct, but none of them is consistently reliable quantitatively. Re-optimization of Lennard-Jones parameters and symmetry-adapted perturbation theory analysis for the benzene dimer suggests that better agreement cannot be expected unless more flexible functional forms (particularly for the electrostatic contributions) are employed for the empirical force fields.
Journal of Physical Chemistry A, 2004
State-of-the-art electronic structure theory has been applied to generate potential energy curves... more State-of-the-art electronic structure theory has been applied to generate potential energy curves for the sandwich, T-shaped, and parallel-displaced configurations of the simplest prototype of aromatic π-π interactions, the benzene dimer. Results were obtained using second-order Møller-Plesset perturbation theory (MP2) and coupled-cluster with singles, doubles, and perturbative triples [CCSD(T)] with different augmented, correlationconsistent basis sets. At the MP2 level, the smallest basis set used (a modified aug-cc-pVDZ basis) underestimates the binding by ∼0.5 kcal mol -1 at equilibrium and by ∼1 kcal mol -1 at smaller intermonomer distances compared to results with a modified aug-cc-pVQZ basis (denoted aug-cc-pVQZ*). The best MP2 binding energies differ from the more accurate CCSD(T) values by up to 2.0 kcal mol -1 at equilibrium and by more than 2.5 kcal mol -1 at smaller intermonomer distances, highlighting the importance of going beyond MP2 to achieve higher accuracy in binding energies. Symmetry adapted perturbation theory is used to analyze interaction energies in terms of electrostatic, dispersion, induction, and exchange-repulsion contributions.
The reliability of density functional theory and other electronic structure methods is examined f... more The reliability of density functional theory and other electronic structure methods is examined for anharmonicities and spectroscopic constants of the ground electronic states of several diatomic molecules. The equilibrium bond length r e , harmonic vibrational frequency e , vibrational anharmonicity e x e , rotational constant B e , centrifugal distortion constant D e , and vibration-rotation interaction constant ␣ e have been obtained theoretically for BF, CO, N 2 , CH ϩ , and H 2 . Predictions using Hartree-Fock, coupled-cluster singles and doubles ͑CCSD͒, coupled cluster singles and doubles with perturbative triples ͓CCSD͑T͔͒, and various density functional methods ͑S-VWN, BLYP, and B3LYP͒ have been made using the 6-31G*, aug-cc-pVDZ, and aug-cc-pVTZ basis sets and compared to experimental values. Density functional theory predictions of the spectroscopic constants are reliable ͑particularly for B3LYP͒ and often perform as well as the more expensive CCSD and CCSD͑T͒ estimates.
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Papers by Mutasem Sinnokrot