VASP, Quantum Espresso, CASTEP, CPMD and ABINIT are the most popular ab initio molecular dynamics software used for calculating and simulating properties of a wide range of materials. The calculation and simulation are based on a quantum-mechanical description of the interactions between electrons and between electrons and atomic nuclei. It promotes a deeper understanding of the materials, and contributes significantly to materials design for future technologies. The five software are all available in the HPC system. You may ask: Which one should I use for my research work?

VASP

Simulations using pseudopotentials or the projector-augmented wave method and a plane wave basis set, VASP computes an approximate solution to the many-body Schrödinger equation, either within the Density Functional Theory (DFT) to solve the Kohn-Sham equation or the Hartree-Fock (HF) approximation to solve the Roothaan equation. Hybrid functionals that mix the HF approach with DFT are implemented, and Green’s functions methods (GW quasi-particles and ACFDT-RPA) and many-body perturbation theory (2nd-order Møller-Plesset) are available in VASP as well.

VASP code depend heavily on the FFTs and Linear Algebra libraries (BLAS/LAPACK/ScaLAPACK). The current version is written in MPI, and OpenMP directives.

VASP has a complete list of pseudopotentials developed for almost all the atoms. It is applicable to the study of structure and phase stability, mechanical and dynamical properties of liquids, glasses and quasicrystals, magnetism and magnetic nanostructures, semiconductors and insulators, surfaces, interfaces and thin films, etc.

Quantum Espresso

  QE is based on density-functional theory, plane waves, and pseudopotentials. The core plane wave DFT functions of QE are provided by the PWscf (Plane-Wave Self-Consistent Field) component, a set of programs for electronic structure calculations within density functional theory and density functional perturbation theory, using plane wave basis sets and pseudopotentials.

QE implements Car-parrinello MD in cp.x where, starting from a ground state wavefunction, the wavefunction for subsequent steps is propagated along the trajectory of the atoms by means of an extended lagrangian scheme.

Users can perform total energy calculations, energy minimization to predict structures, obtain the Kohn-Sham band structure of periodic systems as well as phonons, energy evolution plots, SCF output, cell and force relax, output of stress and forces, simultaneous band structure and phonon calculations.

QE also includes the following more specialized packages which can be used to calculate energy barriers and reaction pathways (PWneb), phonons with Density-Functional Perturbation Theory (PHonton), calculations of spectra using Time-Dependent Density-Functional Perturbation Theory (TDDFPT).

QE package is well documented; many examples are provided for new users to follow and study.

CATEP

The CASTEP program provides a robust and efficient implementation of DFT which is based on the following concepts: Pseudopotential description of the electron-ion interaction; Supercell approach with periodic boundary conditions; Plane wave basis set; Extensive use of fast Fourier transform (FFT) for evaluation of the Hamiltonian terms. It follows the Born-Oppenheimer approximation. i.e. forces are calculated from the ground state electronic configuration at each molecular dynamics step.   Within this scheme the different molecular dynamics ensembles, such as NVE, NVT, NPH, and NPT can be simulated.

CASTEP is a commercial software that comes with Materials Studio software package from Dassault Systems. It can be used to calculate the electronic properties of crystalline solids, surfaces, molecules, liquids and amorphous materials from first principles. As Materials Studio has a very user friendly interface, it is very easy for users to build models and view the calculated results from CASTEP.

CPMD

The CPMD code is a parallelized plane wave and pseudopotential implementation of Density Functional Theory. It is mainly targeted at Car-Parrinello MD simulations, but also supports geometry optimizations, Born-Oppenheimer MD, path integral MD, response functions, QM/MM, excited states and calculation of some electronic properties

The CPMD method is also related to the more common Born–Oppenheimer molecular dynamics (BOMD) method in that the quantum mechanical effect of the electrons is included in the calculation of energy and forces for the classical motion of the nuclei. However, whereas BOMD treats the electronic structure problem within the time-independent Schrödinger equation, CPMD explicitly includes the electrons as active degrees of freedom, via (fictitious) dynamical variables.

Time dependent ab-initio calculations offer a unique window on nanoscale processes. The CPMD code has been used to examine systems including protein active sites, liquid-surface interactions, and surface catalysts. The ability to examine interactions on the nanoscale makes this approach ideal for studying systems where chemical and biological interactions are critical.

In CPMD, the core electrons are usually described by a pseudopotential and the wavefunction of the valence electrons are approximated by a plane wave basis set. The ground state electronic density (for fixed nuclei) is calculated self-consistently, usually using the density functional theory method. Then, using that density, forces on the nuclei can be computed to update the trajectories (using, e.g. the Verlet integration algorithm). In addition, the coefficients used to obtain the electronic orbital functions can be treated as a set of extra spatial dimensions, and trajectories for the orbitals can be calculated in this context.

Abinit

Find the total energy, charge density and electronic structure of systems made of electrons and nuclei (molecules and periodic solids) within Density Functional Theory (DFT), using pseudopotentials and a planewave or wavelet basis.

Excited states can be computed within the Many-Body Perturbation Theory (the GW approximation and the Bethe-Salpeter equation), and Time-Dependent Density Functional Theory (for molecules).

ABINIT also includes the option to optimise the geometry according to the DFT forces and stresses, perform molecular dynamics simulation using these forces, or generate dynamical matrices, bear effective charges, and dielectric tensors based on Density-Functional Perturbation Theory, and many more properties. Computational efficiency is achieved through the use of fast Fourier transforms and pseudopotentials to describe core electrons. Materials that can be treated by ABINIT are insulators, metals, and magnetically ordered systems including Mott Hubbard insulators in the form of molecules, crystals, surfaces and interfaces.

Molecular dynamics simulations are always large calculations, dealing with supercells of hundreds to thousands of atoms. Performance is always a consideration when you choose the software. All five software are coded with MPI and OpenMP parallel libraries, as well as FFT and BLAS/LAPACK libraries. But due to different algorithms used, the performance of different software varies. Dr. Peter Larsson of National Supercomputer Centre at Linköping University did a series of benchmark to compare the performance, scalability and memory usage of VASP and Quantum Espresso, and VASP and Abinit.  He found VASP outperformed both QE and Abinit in speed and scalability:

https://www.nsc.liu.se/~pla/blog/2013/02/04/qevasp-part1
https://www.nsc.liu.se/~pla/blog/2013/02/19/qevasp-part2
https://www.nsc.liu.se/~pla/blog/2013/12/18/qevasp-part3/
https://www.nsc.liu.se/~pla/blog/2012/03/01/abinitvasp-part1/
https://www.nsc.liu.se/~pla/blog/2012/04/18/abinitvasp-part2/

All five software are available on the HPC system. CASTEP comes with the commercial software package Materials Studio and a limited number of licenses. VASP license should be acquired by the researchers directly from the software developer. Abinit, CPMD and Quantum Espresso are open source software and distributed under the GNU General Public License.

Please visit the HPC website for detailed information on accessing these software from the HPC systems: https://comcen.nus.edu.sg/services/hpc/application-software

For users who are going to do material simulation and want to find out which software he should choose, try answering the following questions first:

• Do you have access to the software?

• Is the software well documented? Are tutorials and examples provided?

• Are there any graphic interface for you to build models and input files, and view results?

• How good is the performance and how large can it scale out?

• Are your colleague/supervisor/coworkers also utilizing it?

• Does it have the pseudo potentials for the elements in the system you’ll be studying?

After this, check the literature review of works on similar systems and see what others in the field are using. Also, check if the software is reliable, accurate, high performance and widely accepted.