Improved SCF interaction energy decomposition scheme corrected for basis set superposition effect

Abstract

A modified scheme for SCF interaction energy decomposition has been proposed where the nonphysical basis set superposition error (BSSE) has been corrected by means of the counterpoise method. A new procedure to separate the exchange and induction energy terms free of nonphysical BSSE has been tested in the case of the H20 dimer. The first order BSSE appears to be non-negligible for strong hydrogen bonded complexes. In addition the scheme allows separation of the long-controversial charge-transfer contribution within the induction term, which has been considerably overestimated in previous studies.

Pair interaction energy decomposition analysis

“…For the latter type of dimers DẼ int IJ ¼ DE int IJ , and the same holds for all individual components in eq. (10). In molecular clusters there are no BDAs and no such correction to all properties.…”

“…We took three isomers of polyalanine (ALA) 10 , the helix, turn, and strand (the extended form) capped with acetyl (Ace) and À ÀNHCH 3 groups at the NÀ À and CÀ Àterminus, respectively. All geometries were optimized using the 6-31G* basis set (so that the helix is slightly distorted from being perfectly helical).…”

“…Figure 1. The structures of the systems containing amino acids: (a) the helix of (ALA) 10 , (b) the turn of (ALA) 10 , (c) the strand of (ALA) 10 , and (d) 1L2Y. Fragments are shown in different colors.…”

“…For the turn of (ALA) 10 we extracted two particularly interesting fragment pairs. The first dimer 10-1 features a pair of CÀ ÀH.…”

“…The fragment dipole moments for (ALA) 10 are given in Table 5. The energy decomposition data are summarized in Table 6, Table 7, and Table 8, for the helix, turn, and strand, respectively.…”