Papers by Victor Manuel Velez García
International Journal of Quantum Chemistry, 2019
As part of previous studies, we introduced a new type of basis function named Simplified Box Orbi... more As part of previous studies, we introduced a new type of basis function named Simplified Box Orbitals (SBOs) that belong to a class of spatially restricted functions which allow the zero differential overlap (ZDO) approximation to be applied with complete accuracy. The original SBOs and their Gaussian expansions SBO-3G form a minimal basis set, which was compared to the standard Slater-type orbital basis set (STO-3G). In the present paper, we have developed the SBO basis functions at double-zeta (DZ) level, and we have assessed the option of expanding the SBO-DZ as a combination of Gaussian functions. Finally, we have determined the quality of the new basis set by comparing the molecular properties calculated with SBO-nG with those achieved with some standard basis sets. K E Y W O R D S ab-initio calculations, box orbitals, confined systems, Gaussian expansion, spatially restricted basis functions 1 | INTRODUCTION: SIMPLIFIED BOX ORBITAL AND SIMPLIFIED BOX ORBITAL-nG FUNCTIONS Spatially restricted functions are distinguished as having a value of zero from a certain distance to the center to which they are referred: r > r o) χ(r,θ,ϕ) = 0. This characteristic makes the integrals S pq , H pq , and (pq|rs) zero when the distance between the centers of the two basis functions χ p and χ q is higher than the sum of the radii associated with those two functions. Therefore, it leads to simplifications analogous to those of the zero differential overlap (ZDO) approximation of the semiempirical methods, but in a completely ab-initio context. This advantage has been proven to be useful for improving the computing calculations as shown by the results obtained, for example, with Ramp functions. [1-3] In previous studies based on the pioneering work of Lepetit et al. [4] and Fdez Rico et al., [5-8] we developed a valid spatially restricted basis set for performing calculations on molecules with atoms from H to Kr, but at "single-zeta level." [9-11] In this paper we have developed an Simplified Box Orbital (SBO) basis set at "double-zeta level," which allows calculations to be performed with similar or higher precision than the well-known standard basis set 6-311G(d) of Pople et al. [12] An SBO is a spatially restricted function achieved through the linear combination of terms (r − r o) 3n for the interval 0 < r < r o and with the value of zero outside this interval. SBO r, θ, ϕ ð Þ= R SBO r ð ÞÁΥ m ℓ θ,ϕ ð Þ ð1Þ with the radial part defined as a piecewise function:
Molecular Physics, 2018
Simplified Box Orbitals (SBOs) are a kind of spatially restricted basis functions with a similar ... more Simplified Box Orbitals (SBOs) are a kind of spatially restricted basis functions with a similar use to Slater functions, but fulfilling an exact version of the zero-differential overlap approximation. These functions also allow for a drastic reduction in the number of bielectronic integrals when dealing with huge systems, and can be adapted to study confined systems such as molecules in solution. In previous studies, the necessary SBOs parameters to be used for different elements were defined. However, the accuracy of those basis functions decreases with the atomic number of the atoms under study, and therefore their use was discouraged beyond the Ar atom. In the present study, we verify that slightly increasing the terms of SBOs for a better definition, is enough to correctly handling atoms beyond Ar. This, together with other improvements exposed in this work, allowed obtaining accurate SBOs for K-Kr atoms. To make possible the use of SBOs in standard quantum chemistry calculation software, Gaussian expansions to the proposed basis functions-were achieved. Then, simple formulas for directly obtaining those expansions were deduced. Finally, the results of an SZ basis set of the proposed SBOs are analysed and compared with a similar STO basis set.
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Papers by Victor Manuel Velez García