Energy band method, insufficiency

Ab initio calculations of polymer properties are either simulations of oligomers or band-structure calculations. Properties often computed with ab initio methods are conformational energies, polarizability, hyperpolarizability, optical properties, dielectric properties, and charge distributions. Ab initio calculations are also used as a spot check to verify the accuracy of molecular mechanics methods for the polymer of interest. Such calculations are used to parameterize molecular mechanics force fields when existing methods are insufficient, which does not happen too often. 

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