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Session B02 - Density Functional Methods.
session, Monday morning, June 5, 11:00
Monongahela Room, Westin William Penn Hotel
While widely used in other areas of computational physics, adaptive coordinate grids have not been applied to electronic wave functions, since basis function expansions have proven much more efficient than the finite-element methods conventionally used with such grids. Gygi recently showed that a plane wave expansion basis can be used in conjunction with a continuous curvilinear coordinate transformation which is adaptively parametrized in an unbiased manner. I will describe a full-featured implementation of the local density functional formalism using this transformation, which can be applied to structural energy and band calculations. Wave function expansion coefficients, atom coordinates, and coordinate transformation parameters are all evolved together as dynamical variables to efficiently minimize the total energy. Convergence with basis size is very rapid, compared to ordinary plane waves, for solids containing atoms with highly localized orbitals. The steps of this method will be outlined, and compared with conventional calculations. Extensive tests for convergence, aliasing errors, and spurious interatomic forces mediated by the adaptive coordinates will be discussed. These tests yielded excellent results for crystalline polymorphs of SiO_2 , which form a particularly challenging group of materials for ab initio calculations, and are of considerable technical interest.