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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 conserved enthalpy H (up to numerical inaccuracies). 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 '''


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 an NpH [[Molecular dynamics calculations|molecular-dynamics]] simulation {{TAGO|MDALGO|3}} has to be used. The {{TAG|LANGEVIN_GAMMA}} and {{TAG|LANGEVIN_GAMMA_L}} have to be zero to disable any thermostatting. By setting the tag {{TAGO|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]] will be zero, such that the velocities are determined by the Hellmann-Feynman forces or machine-learned force fields only. Setting the tag {{TAGO|LANGEVIN_GAMMA_L|0}},
the stochastic term of the [[Langevin thermostat]] thermostat will be zero, such that the velocities are determined by the Hellmann-Feynman forces or Machine-learned force fields only.
removes the stochastic term and the friction term from the barostat, resulting in a box update
depending solely on the kinetic stress tensor. The inertia of lattice degrees-of-freedom is controlled with the {{TAG|PMASS}} tag.


{|class="wikitable" style="margin:aut  
{|class="wikitable" style="margin:aut  
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|style="text-align:center;"| {{TAG|LANGEVIN_GAMMA_L}}          ||  style="text-align:center;"|  0         
|style="text-align:center;"| {{TAG|LANGEVIN_GAMMA_L}}          ||  style="text-align:center;"|  0         
|-  
|-  
|style="text-align:center;"| {{TAG|LANGEVIN_GAMMA}}          ||  style="text-align:center;"|  0         
|style="text-align:center;"| {{TAG|LANGEVIN_GAMMA}}          ||  style="text-align:center;"|  0
|-
| optional tags  to set || style="text-align:center;"| {{TAG|PMASS}}        
|}
|}


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 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 [[Andersen thermostat]]''  
''An example {{FILE|INCAR}} file for the NpH ensemble''  


   #INCAR molecular-dynamics tags NVE ensemble  
   #INCAR molecular-dynamics tags NpH ensemble  
   {{TAGBL|IBRION}} = 0                  # choose molecular-dynamics  
   {{TAGBL|IBRION}} = 0                  # choose molecular-dynamics  
   {{TAGBL|MDALGO}} = 1                   # using Andersen thermostat
   {{TAGBL|MDALGO}} = 3                   # using Andersen thermostat
   {{TAGBL|ISIF}} = 2                     # compute stress tensor but do not change box volume/shape  
   {{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|ANDERSEN_PROB}} = 0.0         # setting Andersen collision probability to zero to get NVE enseble
   {{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.}}


==Related tags and articles==
==Related tags and articles==
[[Molecular dynamics calculations|Molecular-dynamics calculations]], {{TAG|ISIF}}, {{TAG|MDALGO}}, [[:Category:Ensembles|Ensembles]]
[[Molecular dynamics calculations|Molecular-dynamics calculations]], {{TAG|ISIF}}, {{TAG|MDALGO}}, {{TAG|LANGEVIN_GAMMA}}, {{TAG|LANGEVIN_GAMMA_L}}, [[:Category:Ensembles|Ensembles]]


[[Category:Molecular dynamics]][[Category:Ensembles]][[Category:Thermostats]]
[[Category:Molecular dynamics]][[Category:Ensembles]][[Category:Thermostats]]

Latest revision as of 10:38, 21 November 2023

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 conserved enthalpy H (up to numerical inaccuracies). 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 MDALGO = 3 has to be used. The LANGEVIN_GAMMA and LANGEVIN_GAMMA_L have to be zero to disable any thermostatting. 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. The inertia of lattice degrees-of-freedom is controlled with the PMASS tag.

NpH ensemble Langevin
MDALGO 3
ISIF 3
LANGEVIN_GAMMA_L 0
LANGEVIN_GAMMA 0
optional tags to set PMASS

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