## Survey

Please consider helping us improve by answering our 3 question survey.

# Qbox: Computing Electronic Structures at the Quantum Level

Qbox is a first-principles molecular dynamics code that is used to compute the electronic structure of atoms, molecules, solids, and liquids within the Density Functional Theory (DFT) formalism. Written to efficiently carry out large simulations on massively parallel supercomputers like Sequoia, Qbox allows researchers to study systems with larger numbers of atoms than most other DFT codes. LLNL’s new version, released in 2012, will let researchers accurately calculate bigger systems on large supercomputers and stay current with the newest methods for accurately describing atoms.

Through Qbox, users can calculate the properties of materials directly from physics equations, rather than from models or by conducting experiments. The DFT quantum mechanical modeling method is used in physics and chemistry to investigate a vast category of physical problems related to the properties of microscopic systems of interacting particles. Using the forces computed within DFT, first-principles molecular dynamics simulations can be carried out keeping either temperature or pressure constant.

Qbox applies some approximations to make calculations computationally feasible. One of the major approximations is the pseudopotential, which replaces the atom with something that acts almost exactly like an atom in a given system of interest but is much faster to compute. Since Qbox was written, users have been coming up with cleverer and more complex ways to build these pseudopotentials to further decrease the computational cost of a given calculation.

Qb@ll is the LLNL version of Qbox being developed by Erik Draeger as an extension of the open-source version of Qbox maintained by code author Francois Gygi at U.C. Davis. Qball 2.0 is a major rewrite of the code that incorporates some newer approaches, including Vanderbilt ultrasoft pseudopotentials, without losing the massive parallelism that is Qbox’s primary distinction from other first-principles materials codes.

For more information, contact Erik Draeger.

**Relevant links**

Thunder’s Power Delivers Breakthrough Science, *Science & Technology Review*, November 2006