Maximum probability domains from Quantum Monte Carlo calculations

Abstract

Abstract:Although it would be tempting to associate the Lewis structures to the maxima of the squared wave function | | 2 , we prefer in this paper the use of domains of the three-dimensional space, which maximize the probability of containing opposite-spin electron pairs. We find for simple systems (CH 4 , H 2 O, Ne, N 2 , C 2 H 2 ) domains comparable to those obtained with the electron localization function (ELF) or by localizing molecular orbitals. The different domains we define can overlap, and this gives an interesting physical picture of the floppiness of CH + 5 and of the symmetric hydrogen bond in FHF − . The presence of multiple solutions has an analogy with resonant structures, as shown in the trans-bent structure of Si 2 H 2 . Correlated wave functions were used (MCSCF or Slater-Jastrow) in the Variational Quantum Monte Carlo framework.

Curly arrows meet electron density transfers in chemical reaction mechanisms: from electron localization function (ELF) analysis to valence-shell electron-pair repulsion (VSEPR) inspired interpretation

“…In molecules, small variations of the basins bounding surfaces off their ELF position increases the variance of the population. The MPDs and the ELF basins are often close one another, except when the MPD approach former approach yields different solutions corresponding to resonant forms 92,107 which are averaged in the ELF partition.…”

Electron density analysis of large (molecular and periodic) systems: A parallel implementation

“…Several schemes have been proposed in the last decades to extract from ρ(r) as much chemical information as possible, which involve its visualization (profiles, 2D maps, 3D graphical representations), partition according to different schemes, topological analysis, etc. [4][5][6][7][8][9][10][11][12][13][14][15] In this respect, one of the most powerful and popular techniques is represented by Bader's quantum theory of atoms in molecules (QTAIM), which relies on the topological analysis of ρ(r). 16 If a routine analysis of the wave-function |Ψ of a small system is a non particularly demanding task from a computational point of view (when compared to the convergence of the self-consistent field, SCF, procedure or to the analytical evaluation of energy gradients), this is clearly no more the case either when rather sophisticated techniques are adopted (such as QTAIM) or when large systems are studied.…”

Six questions on topology in theoretical chemistry

“…I am sceptical about a predictive power of a topological approach, but I see that traditional chemical concepts can be supported by topological approaches. I just mention the recent paper by Arne Lüchow [45], or A. Scemama et al [17], showing that the Lewis electron-pair concept is related to maxima of the squared wave function. Or think of the arrangement of like spins in the valence shell as described by Lennard-Jones [46].…”