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Thursday, October 30, 2014

What is VASP?

The Vienna Ab initio Simulation Package (VASP) is a computer program for atomic scale materials modelling, e.g. electronic structure calculations and quantum-mechanical molecular dynamics, from first principles.

VASP computes an approximate solution to the many-body Schrödinger equation, either within density functional theory (DFT), solving the Kohn-Sham equations, or within the Hartree-Fock (HF) approximation, solving the Roothaan equations. Hybrid functionals that mix the Hartree-Fock approach with density functional theory are implemented as well. Furthermore, Green's functions methods (GW quasiparticles, and ACFDT-RPA) and many-body perturbation theory (2nd-order Møller-Plesset) are available in VASP.

In VASP, central quantities, like the one-electron orbitals, the electronic charge density, and the local potential are expressed in plane wave basis sets. The interactions between the electrons and ions are described using norm-conserving or ultrasoft pseudopotentials, or the projector-augmented-wave method.

To determine the electronic groundstate, VASP makes use of efficient iterative matrix diagonalisation techniques, like the residual minimisation method with direct inversion of the iterative subspace (RMM-DIIS) or blocked Davidson algorithms. These are coupled to highly efficient Broyden and Pulay density mixing schemes to speed up the self-consistency cycle.

 

And what can VASP do?

The following is a (by no means complete) list of VASP features:

Functionals

  • LDA, GGAs, metaGGAs
  • Hartree-Fock, Hartree-Fock/DFT hybrids

First derivatives

  • Forces and stress tensor for DFT, Hartree-Fock, and hybrid functionals

 

Dynamics and relaxation

  • Born-Oppenheimer molecular dynamics
  • Relaxation using conjugate gradient, Quasi-Newton or damped molecular dynamics
  • Nudged elastic band methods (transition states search)
  • Climbing dimer method (transition state search) 

 

Magnetism

  • Collinear and non-collinear
  • Spin-orbit coupling
  • Constrained magnetic moments approach

 

Linear response to electric fields

  • Static dielectric properties
  • Born effective charge tensors
  • Piezoelectric tensors (including ionic contributions)

 

Linear response to ionic displacements

  • Phonons
  • Elastic constants (including ionic contributions)
  • Internal strain tensors

 

Optical properties

  • Frequency dependent dielectric tensors in the independent particle approximation
  • Frequency dependent tensors in the RPA and TD-DFT
  • Cassida's equation for TD-DFT and TD-Hartree-Fock

 

Berry phases

  • Macroscopic polarization
  • Finite electric fields

 

Green's function methods

  • GW quasiparticles
  • ACFDT total energies in the RPA

 

Many-body perturbation theory

  • 2nd-order Møller-Plesset perturbation theory