NpH ensemble: Difference between revisions
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''' Instructions for setting up a NpH ensemble ''' | ''' Instructions for setting up a NpH ensemble ''' | ||
To run | To run an NpH [[Molecular dynamics calculations|molecular-dynamics]] simulation the [[Langevin thermostat]] has to be used. The {{TAG|LANGEVIN_GAMMA}} and {{TAG|LANGEVIN_GAMMA_L|}} have to be zero because otherwise an [[NpT ensemble]] will be simulated. By setting the tag {{TAG|LANGEVIN_GAMMA}}=0 the friction term and | ||
ensemble will be simulated. By setting the tag {{TAG|LANGEVIN_GAMMA}}=0 the friction term and | the stochastic term of the [[Langevin thermostat]] will be zero, such that the velocities are determined by the Hellmann-Feynman forces or machine-learned force fields only. Setting the tag {{TAG|LANGEVIN_GAMMA_L|}}=0, | ||
the stochastic term of the [[Langevin thermostat]] will be zero, such that the velocities are determined by the Hellmann-Feynman forces or | |||
removes the stochastic term and the friction term from the barostat, resulting in a box update | removes the stochastic term and the friction term from the barostat, resulting in a box update | ||
depending solely on the kinetic stress tensor. | depending solely on the kinetic stress tensor. | ||
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It is recommended to equilibrate the system of interest with | It is recommended to equilibrate the system of interest with an [[NpT_ensemble|NPT]] [[Molecular dynamics calculations|molecular-dynamics]] run before starting the NpH run. A general guide for molecular-dynamics simulations can be found on the [[Molecular dynamics calculations|molecular-dynamics]] page. | ||
''An example {{FILE|INCAR}} file for the NpH ensemble'' | ''An example {{FILE|INCAR}} file for the NpH ensemble'' | ||
Revision as of 11:23, 29 August 2022
The NpH ensemble (isoenthalpic–isobaric ensemble) is a statistical ensemble that is used to study material properties under the conditions of a constant particle number N, a pressure p fluctuating around an equilibrium pressure and a enthalpy H fluctuating around an equilibrium value . This page describes how to sample the NpH ensemble from a molecular-dynamics run.
Instructions for setting up a NpH ensemble
To run an NpH molecular-dynamics simulation the Langevin thermostat has to be used. The LANGEVIN_GAMMA and LANGEVIN_GAMMA_L have to be zero because otherwise an NpT ensemble will be simulated. By setting the tag LANGEVIN_GAMMA=0 the friction term and the stochastic term of the Langevin thermostat will be zero, such that the velocities are determined by the Hellmann-Feynman forces or machine-learned force fields only. Setting the tag LANGEVIN_GAMMA_L=0, removes the stochastic term and the friction term from the barostat, resulting in a box update depending solely on the kinetic stress tensor.
| NpH ensemble | Langevin |
|---|---|
| MDALGO | 3 |
| ISIF | 3 |
| LANGEVIN_GAMMA_L | 0 |
| LANGEVIN_GAMMA | 0 |
It is recommended to equilibrate the system of interest with an NPT molecular-dynamics run before starting the NpH run. A general guide for molecular-dynamics simulations can be found on the molecular-dynamics page.
An example INCAR file for the NpH ensemble
#INCAR molecular-dynamics tags NpH ensemble IBRION = 0 # choose molecular-dynamics MDALGO = 3 # using Andersen thermostat ISIF = 3 # compute stress tensor but do not change box volume/shape TEBEG = 300 # set temperature NSW = 10000 # number of time steps POTIM = 1.0 # time step in femto seconds LANGEVIN_GAMMA = 0.0 0.0 # setting friction and stochastic term of Langevin thermostat zero LANGEVIN_GAMMA_L = 0.0 # setting friction and stochastic term of Langevin barostat zero
| Mind: This INCAR file only contains the parameters for the molecular-dynamics part. The electronic minimization or the machine learning tags have to be added. |
Related tags and articles
Molecular-dynamics calculations, ISIF, MDALGO, LANGEVIN_GAMMA, LANGEVIN_GAMMA_L, Ensembles