NpH ensemble: Difference between revisions

From VASP Wiki
No edit summary
No edit summary
Line 1: Line 1:
The [[NpH ensemble]] (isoenthalpic–isobaric ensemble) is a [[:Category:Ensembles|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 calculations|molecular-dynamics]] run.
The [[NpH ensemble]] (isoenthalpic–isobaric ensemble) is a [[:Category:Ensembles|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 <math> \langle p \rangle </math> and a enthalpy H fluctuating around an equilibrium value <math> \langle H \rangle </math>. This page describes how to sample the NpH ensemble from a [[Molecular dynamics calculations|molecular-dynamics]] run.
   
   
''' Instructions for setting up a NpH ensemble '''
''' Instructions for setting up a NpH ensemble '''
Line 34: Line 34:
   {{TAGBL|LANGEVIN_GAMMA}} = 0.0 0.0    # setting friction and stochastic term of Langevin thermostat zero
   {{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
   {{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 15:26, 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 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 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