Environmental influence on electron scattering from a molecule.

The environmental influence on the electron scattering amplitudes of a molecule was evaluated by ab initio molecular-orbital calculations. The model system is formic acid in various states, i.e. the monomer, hydrogen-bonded dimer and ionized formate form. The model electrostatic potentials were calculated either in vacuo or with the polarizable continuum model as a simple model of an aqueous environment. It was found that charge compensation due to the environment affects the scattering amplitudes significantly. The resultant molecular electrostatic potential was fitted by six nucleus-centered Gaussians of site/environment-dependent atomic electrostatic potentials with small residual errors. Therefore, the site/environment-dependent atomic electrostatic potentials will give a good model for electron crystallography.