Density-fitted open-shell symmetry-adapted perturbation theory and application to π-stacking in benzene dimer cation and ionized DNA base pair steps

Abstract

Symmetry-Adapted Perturbation Theory (SAPT) is one of the most popular approaches to energy component analysis of non-covalent interactions between closed-shell systems, yielding both accurate interaction energies and meaningful interaction energy components. In recent years, the full open-shell equations for SAPT up to second-order in the intermolecular interaction and zeroth-order in the intramolecular correlation (SAPT0) were published [P. S. Zuchowski et al., J. Chem. Phys. 129, 084101 (2008); M. Hapka et al., ibid. 137, 164104 (2012)]. Here, we utilize density-fitted electron repulsion integrals to produce an efficient computational implementation. This approach is used to examine the effect of ionization on π-π interactions. For the benzene dimer radical cation, comparison against reference values indicates a good performance for open-shell SAPT0, except in cases with substantial charge transfer. For π stacking between hydrogen-bonded pairs of nucleobases, dispersion interactions still dominate binding, in spite of the creation of a positive charge.

Perspective: Found in translation: Quantum chemical tools for grasping non-covalent interactions

“…Toward achieving that objective, two principle developmental directions emerge: unifying existing approaches to avoid illdefined terms [122][123][124]128 and expanding the field capabilities of existing approaches. 56,124,125,139,179,219,220 The first avenue has already lead to a more stable definition of charge transfer 77,96 or London dispersion terms. 36 Alternatively, SAPT has recently been expanded to treat intramolecular interactions 123,124,128 and open-shell systems.…”

Recent developments in symmetry‐adapted perturbation theory

“…An analogous development based on spin‐unrestricted determinants (UHF/UKS) was carried out by Hapka et al, followed by an efficient density‐fitted implementation of SAPT0(UHF) by Gonthier and Sherrill (see also Reference ). The approaches of References share two limitations. First, they require each monomer to be qualitatively described by a single reference determinant, so they are appropriate only for interactions involving high‐spin open‐shell monomers.…”

“…Second, all unpaired spins in the zeroth‐order wavefunction of References point in the same direction, that is, the quantum number M S for the complex, describing the projection of the total spin angular momentum on the z axis, equals the sum of the respective quantum numbers for the monomers, . Thus, the zeroth‐order wavefunction is a pure, uncontaminated high‐spin state, and the exchange corrections of References are appropriate for the high‐spin state of the dimer, but not for the low‐spin states or for the calculation of spin splittings. For the oxygen dimer example mentioned above, SAPT(ROHF)/SAPT(UHF)/… are capable of describing the interaction in the quintet state, which happened to be one of the first applications of SAPT(ROKS) .…”

Finding chemical concepts in the Hilbert space: Coupled cluster analyses of noncovalent interactions

“…It can be considered as a correction for the higher order terms. Although the accuracy of SAPT0 relies to a large extent on error cancellation, recent implementations of this technique making extensive use of the density‐fitting approximation have reduced the scaling of the method from N 7 to N 5 , thus making it applicable to systems of moderate size (up to 200 atoms and 2,800 basis functions) . More sophisticated SAPT approaches can be defined in which intramolecular correlation corrections to the various SAPT0 terms are included via the use of correlated wavefunction‐based methods or by using density functional theory (DFT) for the description of the monomers, as discussed in the following section.…”