Ab initio Compton maps of small molecules

A closed form expression for the evaluation of directional Compton profiles (DCP) from the position space one-electron reduced density matrix expanded in Cartesian Gaussian basis functions is presented. The Compton map, i.e. a two-dimensional contour plot of the DCP function J(q) in a selected plane , is introduced as a convenient method for describing the DCP anisotropy. S ymmetry properties of J(q) and its multivaluedness at \q \ = 0 are discusse d. Examples of theoretical Compton maps are given for the hydrogen molecule ion (both ground and excited states), water, ammonia, ethylene and (1)A(1) methylene molecules in their ground states. Compton maps generated with Ha rtree- Fock, configuration interaction and density functional theory method s are compared.