A simple natural orbital mechanism of "pure" van der Waals interaction in the lowest excited triplet state of the hydrogen molecule

O.V. Gritsenko, E.J. Baerends

Research output: Contribution to JournalArticleAcademicpeer-review

322 Downloads (Pure)

Abstract

A treatment of van der Waals (vdW) interaction by density-matrix functional theory requires a description of this interaction in terms of natural orbitals (NOs) and their occupation numbers. From an analysis of the configuration-interaction (CI) wave function of the ∑u+3 state of H2 and the exact NO expansion of the two-electron triplet wave function, we demonstrate that the construction of such a functional is straightforward in this case. A quantitative description of the vdW interaction is already obtained with, in addition to the standard part arising from the Hartree-Fock determinant ∫1 σg (r1) 1 σu (r2) ∫, only two additional terms in the two-electron density, one from the first "excited" determinant ∫2 σg (r1) 2 σu (r2) ∫ and one from the state of ∑u+3 symmetry belonging to the (1 π g) 1 (1 π u) 1 configuration. The potential-energy curve of the ∑u+3 state calculated around the vdW minimum with the exact density-matrix functional employing only these eight NOs and NO occupations is in excellent agreement with the full CI one and reproduces well the benchmark potential curve of Kolos and Wolniewicz [J. Chem. Phys. 43, 2429 (1965)]. The corresponding terms in the two-electron density ρ 2 (r1, r2), containing specific products of NOs combined with prefactors that depend on the occupation numbers, can be shown to produce exchange-correlation holes that correspond precisely to the well-known intuitive picture of the dispersion interaction as an instantaneous dipole-induced dipole (higher multipole) effect. Indeed, (induced) higher multipoles account for almost 50% of the total vdW bond energy. These results serve as a basis for both a density-matrix functional theory of van der Waals bonding and for the construction of orbital-dependent functionals in density-functional theory that could be used for this type of bonding. © 2006 American Institute of Physics.
Original languageEnglish
Pages (from-to)054115
JournalJournal of Chemical Physics
Volume124
Issue number5
DOIs
Publication statusPublished - 2006

Fingerprint

Dive into the research topics of 'A simple natural orbital mechanism of "pure" van der Waals interaction in the lowest excited triplet state of the hydrogen molecule'. Together they form a unique fingerprint.

Cite this