Ab initio valence-electron-only molecular electronic structure calculations: Theory and test applications

Abstract

Articles you may be interested inInterpreting ultrafast molecular fragmentation dynamics with ab initio electronic structure calculations Molecular geometry and polarizability of small cadmium selenide clusters from all-electron ab initio and Density Functional Theory calculations A molecular picture of hydrophilic and hydrophobic interactions from ab initio density functional theory calculations Ab initio calculation of the potential surfaces and the electronic transition moments for the valence and Rydberg doublet electronic states of HCO A new method for performing molecular electronic structure calculations using electronic wave functions which make explicit reference only to valence electrons is presented. The method contains nO adjustable parameters and makes use of projection operators to project out the core function space from the valenceelectron wave function. The energy calculated using this valence-electron-only method is guaranteed to converge, with increasing size of orbital basis, upon the valence energy which would be obtained from an equivalent all-electron calculation using a frozen SCF description of the core electrons. The method may be used in conjunction with any desired treatment of the valence-electron wave functions (i.e., SCF, CI, MC-SCF, VB, or VB-SCF). In this paper, test calculations are performed using an SCF treatment of the valenceelectron wave function for the molecules NaCI, Na "and Cl" All-electron and valence-electron-only calculations are compared using differing (i.e., reduced) sizes of orbital basis sets for the valence-electron-only calculations. It is shown that valence-electron-only calculations can lead to considerable savings in computer time while still providing accurate potential energy curves and valence energies.

Theoretical methods for small-molecule ro-vibrational spectroscopy

“…This 'frozen core' approximation is generally accurate [165] and, especially for heavier atoms, considerably simplifies the calculation. However, we would like to point out that this procedure raises some conceptual issues related with electron indistinguishability which need some careful analysis; for a discussion of some of these issues, see [231][232][233][234][235].…”

Formal Analysis of Effective Core Potential Methods

“…It may be noted in passing that the direct use of this approach with an approximation to the core projectors was developed by Leasure et al 16…”