Intrinsic local constituents of molecular electronic wave functions. I. Exact representation of the density matrix in terms of chemically deformed and oriented atomic minimal basis set orbitals

TitleIntrinsic local constituents of molecular electronic wave functions. I. Exact representation of the density matrix in terms of chemically deformed and oriented atomic minimal basis set orbitals
Publication TypeJournal Article
Year of Publication2008
AuthorsIvanic J, Atchity GJ, Ruedenberg K
Journal TitleTheoretical Chemistry Accounts
Volume120
Pages281-294
Date PublishedMay
Type of ArticleProceedings Paper
ISBN Number1432-881X
Accession NumberISI:000256308800023
KeywordsBONDING SCHEMES, CONVERGENCE, DEADWOOD, DIRECT CONFIGURATION-INTERACTION, FORS MODEL, LOCALIZATION, NATURAL, orbitals, QUANTUM-THEORY, SPACES, WAVEFUNCTIONS
Abstract

A coherent, intrinsic, basis-set-independent analysis is developed for the invariants of the first-order density matrix of an accurate molecular electronic wave function. From the hierarchical ordering of the natural orbitals, the zeroth-order orbital space is deduced, which generates the zeroth-order wavefunction, typically an MCSCF function in the full valence space. It is shown that intrinsically embedded in such wavefunctions are elements that are local in bond regions and elements that are local in atomic regions. Basis-set-independent methods are given that extract and exhibit the intrinsic bond orbitals and the intrinsic minimal-basis quasi-atomic orbitals in terms of which the wavefunction can be exactly constructed. The quasi-atomic orbitals are furthermore oriented by a basis-set independent method (viz. maximization of the sum of the fourth powers of all off-diagonal density matrix elements) so as to exhibit clearly the chemical interactions. The unbiased nature of the method allows for the adaptation of the localized and directed orbitals to changing geometries.

DOI10.1007/s00214-007-0308-4
Alternate JournalTheor. Chem. Acc.