Abstract
Theoretical description of molecular interactions remains a challenge for computational chemistry. In particular, systems dominated by static correlation, in which bonds are stretched or twisted, are often beyond capabilities of methods based on a single-electron approximation, being usually a method of choice. For interacting multireference systems, it is necessary to apply either high-level coupled-cluster methods (which however include multireference effects only partially) or base the theoretical description on a multireference wavefunction. Popular multireference methods like CASPT2 (complete active space perturbation theory) do not provide satisfactory results since they may suffer from problems with size consistency and poor accuracy. Recently we have shown that combining a simple multireference wavefunction, perfect-pairing generalized valence bond (GVB) with extended random phase approximation in embedding framework (EERPA) leads to a method EERPA-GVB providing accurate results for challenging multireference systems. In this paper, good performance of EERPA-GVB is confirmed by its application to van der Waals and hydrogen-bonded complexes. In addition, we show that the decomposition of the EERPA-GVB correlation energy into contributions from pairs of geminals can provide useful insight into the investigated interactions.
Highlights
The ubiquity of non-covalent interactions and their increasingly appreciated role in such fields as material design [1], catalysis [2], medicine [3] and even photochemistry [4,5,6] necessitates the development of computational tools able to describe them
We firstly recap the theoretical framework of extended random phase approximation in embedding framework (EERPA)-generalized valence bond (GVB), we show the method’s robustness using examples of dispersion-dominated and hydrogen-bonded dimers, and we analyze the behavior of two van der Waals complexes with twisted or broken bonds
One could wonder whether—if the basis set used is sufficiently large—the counterpoised corrected Extended Random Approximation (ERPA) and EERPA methods would produce the same results. This is, not the case, since the correlation effects included in EERPA are missed in ERPA and this is not related to the basis set size
Summary
The ubiquity of non-covalent interactions and their increasingly appreciated role in such fields as material design [1], catalysis [2], medicine [3] and even photochemistry [4,5,6] necessitates the development of computational tools able to describe them. It has been a challenge, in particular due to the long-range nature and the subtlety of the London dispersion, but recently sophisticated coupledcluster approaches are becoming more computationally affordable [7, 8] and efficient approaches such as the density functional theory (DFT) [9] have developed ways to treat.
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