Molecular electron momentum density

Several review articles on the theoretical aspects of electron momentum densities of atoms and molecules were written in the 1970s by Benesch and Smith [9], Epstein [10,11], Mendelsohn and Smith [12], Epstein and Tanner [13], Lindner [14], and Kaijser and Smith [15]. Since that time (e,2e) spectroscopy and the momentum densities of Dyson orbitals have been reviewed very often [16-28]. However, to my knowledge, a review article on molecular electron momentum densities has not been written recently apart from one [29] devoted solely to the zero-momentum critical point. The purpose of this chapter is to survey what is known about the electron momentum density of atoms and molecules, and to provide an extensive, but not exhaustive, bibliography that should be sufficient to give a head start to a nonspecialist who wishes to enter the field. 

Indices of molecular similarity and dissimilarity based on the electron momentum density have been found useful by Allan, Cooper and coworkers [388-393] and Ho et al. [394]. 

Fig. 19.4. Surface plots of the electron momentum density of H2 illustrating a (3, — 3) maximum alp — Q. The left and right plots are in planes parallel and perpendicular to the molecular axis 0,pj and n p, py, 0),...

Bonds with r < dl < d[ become possible because of nuclear screening (increased bond order), which causes concentration of the bonding pair directly between the nuclei. The exclusion limit is reached at d = t and appears as a geometrical property of space. The distribution of molecular electron density is dictated by the local geometry of space-time. Model functions, such as VSEPR or minimum orbital angular momentum [65], that correctly describe this distribution, do so without dictating the result. The template is provided by the curvature of space-time which appears to be related to the three fundamental constants tt, t and e. 

Cooper and Allan ° have used momentum density in several studies. A problem remains in obtaining the momentum space densities because most calculations are performed with position space wave functions. In a sense, working in momentum space is yet another way to reduce the overweighting of the core electron density. Most of the following discussions on, e.g., molecular alignment and quantum similarity indices, remain valid when we... 

Allan, N.L. and Cooper, D. Momentum-Space Electron Densities and Quantum Molecular Similarity. 173, 85-111 (1995). 

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