Mo/ller–Plesset perturbation investigation of the He2 potential and the role of midbond basis functions

Abstract

The Mo/ller–Plesset perturbation theory up to the complete fourth order is applied to calculate the ab initio van der Waals energy potential of He2. A scheme of constructing a very efficient basis set is proposed based on theoretical considerations. Such a basis set contains a set of Gaussian functions (usually of low angular momentum) centered at the midbond of the van der Waals molecule, which have been proven very efficient to reproduce the intersystem correlation interaction energy normally to be achieved by use of the nucleus-centered high angular momentum polarization functions. A nuclear-centered moderate set [5s4p2d] augmented by a set of midbond functions such as {3s3p2d} produces a value of 10.04 K for the well depth of He2 at the complete fourth-order (MP4) theory. Results from a series of other basis sets suggest that this value is nearly saturated with the further increase of basis, which is in agreement with the estimate of the complete basis-set limit. Calculations of the potential at the minimum and the other distances (3.0–10.0 a0) confirm that the MP4 method, together with the use of midbond functions, is a reliable and convenient choice for the accurate calculations.

Linewidths of C2H2 perturbed by H2: experiments and calculations from an ab initio potential

“…We add to this Sadlej set a polarization orbital "d" for the H atoms taken from the aug-cc-pVTZ basis set to obtain [3s2p1d] contracted Gaussian functions for H atoms and [5s3p2d] for C atoms. In all cases, mid-bond functions as proposed by Tao and Pan [47] To test the influence of the choice of the ab initio method and of the basis set, we have conducted potential energy calculations for specific conformations (R, θ A , θ B , φ) of the C 2 H 2 -H 2 dimer where (R, θ A , θ B , φ) are the four angular Jacobi coordinates which describe the relative orientation of the two monomers. R is the distance between the two monomer centers of mass and defines the intermolecular axis, θ {A,B} defines the bending angle of the monomer axis relative to the intermolecular axis (the "A" index refers to C 2 H 2 while "B" refers to H 2 ) and φ is the rotational angle around R of one monomer relative to the other.…”

Predicting atomic dopant solvation in helium clusters: The MgHen case

“…Funk et al performed MP4 computations adopting a basis set derived from Huzinaga et al [24] and augmented with diffuse functions; these authors provided a well depth estimate of 4.54 cm −1 at the Mg-He internuclear distance of 5.16Å. Partridge et al carried out CCSD(T) computations with the aug-cc-pVQZ basis set for both He and Mg [25], supplemented with the 332 set of bond functions proposed by Tao and Pan [26]. They obtained a well depth of 4.76 cm −1 at the distance of 5.09Å.…”

“…[31], and the basis set proposed by Archibong and Takkar [32]. We also tested the effect of including bond functions, placed at midway between helium and magnesium, using alternatively the 332 set of Tao and Pan [26] and the 33221 set by Cybulski and Toczylowski [33].…”

Rotational excitation of methylidynium (CH+) by a helium atom at high temperature

“…All our calculations were performed with the augmented correlation consistent valence quadruple zeta (aVQZ) basis set of Woon & Dunning (1994) for all atoms. The (3s3p2d1f) set of bond functions defined by Tao & Pan (1992) are added and placed at mid-distance between the c.m. of CH + and He.…”