Session S15 - Materials Theory and Simulation V.
FOCUS session, Wednesday afternoon, March 14
Room 211, Washington State Convention Center
We have implemented a method to perform standard density-functional calculations with CPU time and memory requirements that scale linearly with the system size, allowing calculations with thousands of atoms on a workstation. Exchange and correlation are treated within the local spin density or gradient-corrected approximations, and we use Troullier-Martins norm-conserving pseudopotentials in the Kleinman-Bylander form.
The basis set of atomic orbitals can be constructed from numerical solutions of the atomic pseudopotential, while they are constrained to be zero beyond a cutoff radius. Further improvements can be made by optimizing their radial shape for the chemical environment. Multiple-zeta and polarization orbitals can be included to achieve an arbitrarily rich basis set, and an accuracy comparable to that of plane-waves.
The basis orbitals are projected on a uniform real-space grid in order to calculate the electron density and the Hartree and exchange-correlation potentials and matrix elements. Other matrix elements, like those of the kinetic energy and nonlocal pseudopotentials are tabulated as two-center integrals.
Electron wave functions need not be explicitly orthogonalized. Instead, we use a modified energy functional, whose minimization produces orthogonal wave functions and the same energy and density as the Kohn-Sham functional. Additionally, confining the Wannier-like electron wave functions to a finite region allows the linear scaling of CPU time and memory, while the error introduced decreases rapidly with the confinement radius.
Forces and stresses are also calculated efficiently and accurately, thus allowing structural relaxation and molecular dynamics simulations.
I will briefly review some applications in physical, chemical, and biological systems.
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