%0 DATA
%A Qingchun, Wang
%A Jingxiang, Zou
%A Enhua, Xu
%A Peter, Pulay
%A Shuhua, Li
%D 2018
%T Automatic Construction of the Initial Orbitals for Efficient Generalized Valence Bond
Calculations of Large Systems
%U https://acs.figshare.com/articles/journal_contribution/Automatic_Construction_of_the_Initial_Orbitals_for_Efficient_Generalized_Valence_Bond_Calculations_of_Large_Systems/7445834
%R 10.1021/acs.jctc.8b00854.s002
%2 https://ndownloader.figshare.com/files/13783094
%K singlet ground state
%K RHF
%K HF
%K Efficient Generalized Valence Bond Calculations
%K UNO
%K scheme II
%K KM
%K black-box GVB calculations
%K optimized GVB wave function
%K orbital
%K GAMESS
%X We propose an efficient general strategy
for generating initial
orbitals for generalized valence bond (GVB) calculations which makes
routine black-box GVB calculations on large systems feasible. Two
schemes are proposed, depending on whether the restricted Hartree–Fock
(RHF) wave function is stable (scheme **I**) or not (scheme **II**). In both schemes, the first step is the construction of
active occupied orbitals and active virtual orbitals. In scheme **I**, active occupied orbitals are composed of the valence orbitals
(the inner core orbitals are excluded), and the active virtual orbitals
are obtained from the original virtual space by requiring its maximum
overlap with the virtual orbital space of the same system at a minimal
basis set. In scheme **II**, active occupied orbitals and
active virtual orbitals are obtained from the set of unrestricted
natural orbitals (UNOs), which are transformed from two sets of unrestricted
HF spatial orbitals. In the next step, the active occupied orbitals
and active virtual ones are separately transformed to localized orbitals.
Localized occupied and virtual orbital pairs are formed using the
Kuhn–Munkres (KM) algorithm and are used as the initial guess
for the GVB orbitals. The optimized GVB wave function is obtained
using the second-order self-consistent-field algorithm in the GAMESS
program. With this procedure, GVB energies have been obtained for
the lowest singlet and triplet states of polyacenes (up to decacene
with 96 pairs) and the singlet ground state of two di-copper–oxygen–ammonia
complexes. We have also calculated the singlet–triplet gaps
for some polyacenes and the relative energy between two di-copper–oxygen–ammonia
complexes with the block-correlated second-order perturbation theory
based on the GVB reference.