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### Electronic Structure - quantum mechanics of solids

Density-functional theory (DFT) is widely used to describe the
electronic structure of crystalline solids. I've worked with Jeff
Nelson and others at Sandia to parallelize Car-Parinello DFT codes
that represent electron wave functions with plane-wave basis
sets. These codes are best suited to modeling materials with
smoothly-varying valence states such as semiconductors and
metals. Core electron states are represented with compute-efficient
pseudo- potentials.

Plane-wave DFT codes require parallel FFTs to swap between real-space
and reciprocal-space representations of various operators. Our work on
parallel FFTs is described here. Other parallel issues
addressed in the codes include Gram-Schmidt orthonormalization of a
large set of wave functions and load- balancing issues that arise from
working on 2 different data sets -- one for the full 3-d FFT mesh and
one for the spherical subset of mesh points that correspond to wave
vectors whose length is within a cutoff distance. We devised a novel
way of mapping back and forth between these 2 data sets to maintain
load-balance in each stage of the computation; it's described in the
1993 PRB paper below.

Collaborators on this project:

- Jeff Nelson, Sandia
- Alan Wright, Sandia

These papers describe various aspects of the DFT work. The book
chapter is the most recent and includes some discussion of our FFT
methodology. The 1995 PRB article is an application of the code to
amorphous carbon (other calcuations can be found by a literature
search for J. S. Nelson or A. F. Wright articles). The earlier 1993
PRB article was our first explanation of our parallel strategy for
plane-wave DFT codes.

**Plane-wave Psuedopotential Electronic Structure Calculations on Parallel
Supercomputers**, J. S. Nelson and S. J. Plimpton, chapter in Topics in
Computational Materials Science, edited by C. Y. Fong, published by World
Scientific, 61-95 (1998). (abstract)

**Basis-Set Convergence of Highly Defected Sites in Amorphous-Carbon**,
J. S. Nelson, E. B. Stechel, A. F. Wright, S. J. Plimpton,
P. A. Schultz, M. P. Sears, Phys Rev B, 52, 9354-59
(1995). (abstract)

**Plane-wave Electronic- Structure Calculations on a Parallel
Supercomputer**, J. S. Nelson, S. J. Plimpton, M. P. Sears, Phys Rev
B, 47, 1765-1774 (1993). (abstract)