Abstract
An algorithm to solve the Huzinaga subsystem self-consistent field equations is proposed using two approximations: a local expansion of subsystem molecular orbitals and a truncation of the projection operator. Test calculations are performed on water and ammonia clusters, and n-alkane and poly-glycine. The errors were 2.2 and -0.6 kcal/mol for (H2O)40 and C40H82, respectively, at the Hartree-Fock level with the 6-31G basis set.
Highlights
Several other groups of methods bear some similarity to these approaches: divide-and-conquer methods,14 especially in the formulation relying on an explicit use of subsystems;15,16 group self-consistent field (SCF),17 atoms-in-molecules,18 and valence bond methods;19 approaches based on electron densities of subsystems;20,21 subsystem or partition density methods with fractional occupations;22,23 SCF for molecular interactions and similar approaches24,25 and fragmentation methods
Test molecules (H2O)n, (NH3)n, n-alkane (n-CnH2n+2), and poly-glycine capped with an acetyl group (Ace) at the N-terminus and a N-methyl amide group (NMe) at the C-terminus (Ace(GLY)n-NMe) are chosen for test systems of group molecular orbitals (GMOs) calculations
The group molecular orbital method has been proposed to solve the Huzinaga subsystem SCF equations with some approximations to reduce the computational scale for large molecular systems
Summary
In which wave functions of subsystems are obtained using self-consistent field (SCF) are applied to determine localized orbitals, define model core potentials (core and valence electrons in an atom are treated as subsystems) and efficiently treat large molecular systems.. Charge transfer between subsystems can be ignored in some methods, or obtained from unions of subsystems or with fractional occupations.. A number of methods utilize either a many-body expansion or use a thermodynamic subtraction scheme removing double counting.. The method is selfconsistent, employs global embedding, does not use caps (except in the construction of the initial density), and charge transfer is accounted for by using overlapping subsystems. Neither a many-body expansion nor a subtraction scheme is used
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