NpH ensemble: Difference between revisions
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To run a NpH [[Molecular dynamics calculations|molecular-dynamics]] run the [[Langevin thermostat]] has to be used. The {{TAG|LANGEVIN_GAMMA}} and {{TAG|LANGEVIN_GAMMA_L|}} have to be zero because otherwise a NpT | To run a NpH [[Molecular dynamics calculations|molecular-dynamics]] run the [[Langevin thermostat]] has to be used. The {{TAG|LANGEVIN_GAMMA}} and {{TAG|LANGEVIN_GAMMA_L|}} have to be zero because otherwise a NpT | ||
ensemble will simulated. By setting the tag {{TAG|LANGEVIN_GAMMA}}=0 the friction term and | ensemble will simulated. By setting the tag {{TAG|LANGEVIN_GAMMA}}=0 the friction term and | ||
the stochastic term of the [[Langevin thermostat]] | 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, | ||
removes the stochastic term and the friction term from the barostat, resulting in a volume update | |||
depending solely on the kinetic stress tensor. | |||
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#INCAR molecular-dynamics tags NVE ensemble | #INCAR molecular-dynamics tags NVE ensemble | ||
{{TAGBL|IBRION}} = 0 # choose molecular-dynamics | {{TAGBL|IBRION}} = 0 # choose molecular-dynamics | ||
{{TAGBL|MDALGO}} = | {{TAGBL|MDALGO}} = 3 # using Andersen thermostat | ||
{{TAGBL|ISIF}} = | {{TAGBL|ISIF}} = 3 # compute stress tensor but do not change box volume/shape | ||
{{TAGBL|TEBEG}} = 300 # set temperature | {{TAGBL|TEBEG}} = 300 # set temperature | ||
{{TAGBL|NSW}} = 10000 # number of time steps | {{TAGBL|NSW}} = 10000 # number of time steps | ||
{{TAGBL|POTIM}} = 1.0 # time step in femto seconds | {{TAGBL|POTIM}} = 1.0 # time step in femto seconds | ||
{{TAGBL| | {{TAGBL|LANGEVIN_GAMMA}} = 0.0 0.0 # setting friction and stochastic term of Langevin thermostat zero | ||
{{TAGBL|LANGEVIN_GAMMA_L}} = 0.0 # setting friction and stochastic term of Langevin barostat zero | |||
{{NB|mind| This {{FILE|INCAR}} file only contains the parameters for the molecular-dynamics part. The [[Electronic minimization|electronic minimization]] or the [[Machine-learned force fields|machine learning]] tags have to be added.}} | {{NB|mind| This {{FILE|INCAR}} file only contains the parameters for the molecular-dynamics part. The [[Electronic minimization|electronic minimization]] or the [[Machine-learned force fields|machine learning]] tags have to be added.}} | ||
Revision as of 13:29, 11 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 p and a enthalpy H fluctuating around an equilibrium value H. This page describes how to sample the NpH ensemble from a molecular-dynamics run.
Instructions for setting up a NpH ensemble
To run a NpH molecular-dynamics run the Langevin thermostat has to be used. The LANGEVIN_GAMMA and LANGEVIN_GAMMA_L have to be zero because otherwise a NpT ensemble will 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 volume 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 a NPT molecular-dynamics run. A general guide for molecular-dynamics simulations can be found on the molecular-dynamics page.
An example INCAR file for the Andersen thermostat
#INCAR molecular-dynamics tags NVE 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. |