A new orbital-based model for the analysis of experimental molecular charge densities: an application to (Z)-N-methyl-C-phenylnitrone.

An alternative to the usual atom-centred multipole expansion is presented for the analysis of high resolution, low-temperature X-ray scattering data. The molecular electron density is determined in a fixed basis of molecular orbitals with variable orbital occupation numbers, i.e. the same form which is used to represent the density in ab initio electron-correlated calculations. The advantages of such an approach include linear scaling (in the sense that the number of parameters to be determined by fitting varies linearly with system size) and ease of property calculation. The method is applied to experimental high-resolution structure factors for a phenylnitrone, and compared to the results of a multipole model of the same data. Finally, the model is critically compared with several related, published orbital-based models.