Abstract
This paper presents the results of a pioneering exploration of the physical origins of vibrational contributions to the interaction-induced electric properties of molecular complexes. In order to analyze the excess nuclear relaxation (hyper)polarizabilities, a new scheme was proposed which relies on the computationally efficient Bishop-Hasan-Kirtman method for determining the nuclear relaxation contributions to electric properties. The extension presented herein is general and can be used with any interaction-energy partitioning method. As an example, in this study we employed the variational-perturbational interaction-energy decomposition scheme (at the MP2/aug-cc-pVQZ level) and the extended transition state method by employing three exchange-correlation functionals (BLYP, LC-BLYP, and LC-BLYP-dDsC) to study the excess properties of the HCN dimer. It was observed that the first-order electrostatic contribution to the excess nuclear relaxation polarizability cancels with the negative exchange repulsion term out to a large extent, resulting in a positive value of Δα(nr) due to the contributions from the delocalization and the dispersion terms. In the case of the excess nuclear relaxation first hyperpolarizability, the pattern of interaction contributions is very similar to that for Δα(nr), both in terms of their sign as well as relative magnitude. Finally, our results show that the LC-BLYP and LC-BLYP-dDsC functionals, which yield smaller values of the orbital relaxation term than BLYP, are more successful in predicting excess properties.
Highlights
Skwara et al.[23] performed the decomposition of the excess electric properties of the linear HF dimer into interaction energy components
Since the seminal work of Morokuma, who was the first to introduce a robust scheme for the decomposition of supermolecular interaction energy into physically meaningful components based on analysis and interpretation of the Fock matrix elements,[61] many similar approaches have been proposed including the extended transition state (ETS) method of Ziegler and Rauk,[62] the improved Kitaura–Morokuma (KM) scheme,[63] the constrained space orbital variation (CSOV),[64] the reduced variational space self-consistent field (RVS-SCF),[65] the natural energy decomposition analysis (NEDA),[66] the block-localized wavefunction approach (BLW-ED)[67] and the method recently proposed by Su and Li.[68]
The concept of excess properties is a convenient framework to gain insight into the effect of intermolecular interactions on the electric properties of molecular complexes and clusters, which can be relevant to set up appropriate models for calculations of bulk properties
Summary
Skwara et al.[23] performed the decomposition of the excess electric properties (dipole moment, polarizability and first hyperpolarizability) of the linear HF dimer into interaction energy components They highlighted a subtle balance of the electrostatic and exchange repulsion contributions. Gora et al studied the excess electric properties of a set of hydrogen-bonded systems, encompassing quasi-linear dimers of hydrogen cyanide, urea, diformamide, 4-pyridone, 4-nitroaniline, and the complex of hydrogen fluoride with nitroacetylene.[27,40] These authors found that the origins of the interaction-induced dipole moment are purely electrostatic in nature with only a minor contribution. A quite different approach is the concept of the (hyper)polarizability densities developed by Nakano and coworkers,[51,52,53] which are defined as the derivatives of the Mulliken charge densities with respect to the electric field Their (hyper)polarizability density plots allow the visualization of the local contributions to the total properties. The HCN dimer is chosen as a model system for this purpose, mainly because its electronic excess properties were already thoroughly studied in our previous paper.[27]
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