A Simple Approach to Nonspherical Electron Densities by Using Invarioms

摘要

The Hohenberg-Kohn theorem highlights the importance of the electron density ρ(r) as a fundamental physical property that uniquely characterizes an electronic system. It states that the ground-state energy of a nondegenerate quantum chemical system is a function of the electron density. The electron density of a crystalline state can, in principle, be measured by high-resolution X-ray diffraction. In spite of the significantly improved experimental conditions (availability of area detectors, synchrotron radiation, and low-temperature devices), the collection of high-resolution data (d≤0.5 A or sin θλ~(-1)≥1.0 A~(-1)) - prerequisite for X-ray charge density studies - remains technically difficult, especially for biopolymers, such as proteins, that usually form soft crystals of low scattering power. Owing to their size, the applicability of ab initio calculations to this important class of compounds is also limited.