Non-empirical Calculations of the Geometry and Conformations of Polyatomic Molecules

Non-empirical methods for the calculation of the geometry, barriers to internal rotation, and conformation energies of polyatomic molecules are discussed. It is shown that the geometry can be predicted with adequate accuracy by calculations with "moderate" basis sets. Reliable estimations of barriers to internal rotation and of conformational energies require in general considerably larger basis sets. Several procedures for combining quantum-mechanical integrals are considered and the "nature" of the barriers is analysed from this standpoint.
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