## ABINIT

### ABINIT

#### Overview:

ABINIT is a first principles pseudopotential code that can be used to model materials from the atoms up. It has the ability to examine systems such as molecules, crystals, surfaces, and interfaces.

#### Applications:

First principles or ab-initio approaches provide a method for modeling systems based solely on their atomic coordinates and the Z numbers of the different atoms. These techniques rely on the fact that there should be one unique charge density or distribution which describes the ground state of a system. This reduces the problem of solving for the electronic structure of a system from a 3N dimensional problem to one that only depends on the charge density. A number of approaches have been developed to properly reduce a system to the minimum energy electronic configuration and ABINIT includes several of these.

First principles codes such as ABINIT have proved useful to topics ranging from the composition of the planetary core to the electrical properties of single molecules. ABINIT can calculate the forces on atoms in a structure and use this information to relax the system. This has provided critical understanding in how surfaces reconstruct, how absorbates interact with surface sites, and how magnetic impurities affect neighbor lattice sites. Typically calculations can consider 30-40 atoms comfortably. Larger systems can be done, but for fairly large systems (greater than 150 atoms), parallel calculations are essential.

In addition to minimizing the total energy of a structure, ABINIT can also calculate band structures, density of states, magnetic properties, and phonon dispersion curves. The code is open source and it is available for many different operating systems. Please start at the ABINIT home page to learn more about this versatile code.

#### Developers:

Xavier Gonze and many others

#### Getting Started:

- Program Webpage: www.abinit.org
- ABINIT New User Guide (Online Version)
- ABINIT Tutorials (Developed by the ABINIT team)
- Lesson 1: H2 molecule - total energy, charge density, bond length, and more
- Lesson 2: H2 molecule - convergence studies, LDA versus GGA
- Lesson 3: Crystalline silicon - k-point grids, computation of band structure, and convergence for an insulator
- Lesson 4: Crystalline aluminum - surface calculations, Fermi distributions, surface energy and convergence issues

- Running ABINIT on the Nanolab Cluster

#### Relevant Research Articles and Webpages:

M. C. Payne, M. P. Teter, D. C. Allan, T. A. Arias, and J. D. Joannopoulos, "Iterative minimization techniques for ab-initio total energy calculations: molecular dynamics and conjugate grandients", Review of Modern Physics, 64, 1045 (1992).

X. Gonze, J.-M. Beuken, R. Caracas, F. Detraux, M. Fuchs, G.-M. Rignanese, L. Sindic, M. Verstraete, G. Zerah, F. Jollet, M. Torrent, A. Roy, M. Mikami, Ph. Ghosez, J.-Y. Raty, D. C. Allan, "First principles computation of material properties: the ABINIT software project", Computational Materials Science, 25, 478, (2002).

#### Questions, Comments...

Please contact:

Derek Stewart, Ph.D.

stewart (at) cnf.cornell.edu

Cornell Nanoscale Facility