Cpmd

Car–Parrinello molecular dynamics or CPMD usually refers to either the computational chemistry software package CPMD, a parallelized plane wave / pseudopotential implementation of density functional theory, particularly designed for ab initio molecular dynamics,[1] or the underlying theory known as the Car–Parrinello method,[2] which is 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, but 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.

General approach

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, however, 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.

Fictitious dynamics

CPMD is an approximation of the Born–Oppenheimer MD (BOMD) method. In BOMD the electrons' wavefunction must be minimized via matrix diagonalization at every step in the trajectory. CPMD uses fictitious dynamics to keep the electrons close to the ground state, preventing the need for a costly self-consistent iterative minimization at each time step. The fictitious dynamics relies on the use of a fictitious electron mass (usually in the range of 400 – 800 a.u.) to ensure that there is very little energy transfer from nuclei to electrons, i.e. to ensure adiabaticity. Any increase in the fictitious electron mass resulting in energy transfer would cause the system to leave the ground-state BOMD surface.[3]

See also

References

External links

  • http://www.cpmd.org/
  • http://www.cpmd.org/documentation/useful-linksTemplate:Theoretical-chem-stub
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