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XIII. Charge Deformation and Vibrational Smearing
Author(s) -
Hirshfeld F. L.
Publication year - 1977
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.197700029
Subject(s) - chemistry , charge (physics) , vibration , deformation (meteorology) , motion (physics) , fourier transform , convolution (computer science) , atomic physics , charge density , effective nuclear charge , computational physics , computational chemistry , classical mechanics , molecular physics , quantum mechanics , physics , ion , organic chemistry , machine learning , meteorology , artificial neural network , computer science
A tractable model for treating the vibrational smearing is provided by the convolution approximation, which divides the molecular charge into fragments that are assumed to move rigidly with the atomic nuclei. This model is of questionable validity for internal vibrations, the required charge decomposition is largely arbitrary, the atomic vibration amplitudes may not be well determined and rotational motion introduces special difficulties. These deficiencies are especially severe if we attempt, by means of a charge deformation model and least‐squares refinement, to derive static charge density maps from the X‐ray data. The greatest uncertainty occurs at the nuclear positions, around hydrogen atoms, or in groups undergoing large librational motion. Yet with suitable caution and a well tested deformation model, least‐squares refinement can yield more detailed and dependable charge‐density information than can Fourier methods.