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 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]] simulation 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 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 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
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 a [[NpT_ensemble|NPT]] [[Molecular dynamics calculations|molecular-dynamics]] run. A general guide for molecular-dynamics simulations can be found on the [[Molecular dynamics calculations|molecular-dynamics]] page.
It is recommended to equilibrate the system of interest with a [[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 13:31, 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 simulation the Langevin thermostat has to be used. The LANGEVIN_GAMMA and LANGEVIN_GAMMA_L have to be zero because otherwise a 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 a 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 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.

Related tags and articles

Molecular-dynamics calculations, ISIF, MDALGO, Ensembles