Sparse matrix based implementation of the DFTB method

Bálint Aradi1, Ben Hourahine, benjamin.hourahine@strath.ac.uk2,
Christof Köhler, c.koehler@phys.uni-paderborn.de1, and Thomas
Frauenheim, frauenheim@phys.upb.de1. (1) Bremen Center for
Computational Materials Science, Bremen University, Bibliotheksstrasse
1, Bremen, 28359, Germany, (2) SUPA, Department of Physics, The
University of Strathclyde, John Anderson Building, 107 Rottenrow,
Glasgow, G4 0NG, United Kingdom

A new Fortran 95 implementation of DFTB (Density Functional based
Tight Binding) has been developed. Unlike previous versions of this
method, the sparsity of the DFTB system of equations has been
exploited. Conventional dense algebra is only used to evaluate the
eigenproblems of the system and long-range Coulombic terms, but
drop-in O(N) or O(N2) modules are planned to replace the small code
sections these entail. The new features include spin polarisation,
efficient molecular and periodic boundary conditions (including
k-points) and LDA+U in the DFTB approximation. The user interface had
been completely replaced with a new extensible and human friendly
input format. The structure of the new implementation was designed to
be modular in order to allow developers an easy extending and
embedding of the code. An overview and some benchmark details of the
new code will be presented and some further planned developments will
be discussed.