NVE ensemble: Difference between revisions

Revision as of 14:41, 20 July 2022

The NVE ensemble (micro-canonical ensemble) is a statistical ensemble that is used to study material properties under the conditions of a constant particle number N, constant volume V and an internal energy E fluctuating around an equilibrium value E. This page describes how to sample the NVE ensemble from a molecular-dynamics run.

Instructions for setting up a NVE ensemble

There are two choices of thermostats which can be adjusted to set up a molecular-dynamics run. The Andersen thermostat can be used by setting the collision probability (ANDERSEN_PROB) with the fictitious heat bath to zero and the Nose-Hoover thermostat by setting the mass of the virtual degree to minus three. Both settings will switch the thermostat of such that the velocities are determined by the Hellmann-Feynman forces or Machine-learned force fields only. See table for the corresponding MDALGO setting and related tags.

NVE ensemble	Andersen	Nose-Hoover
MDALGO	1	0 or 2
additional tags to set	ANDERSEN_PROB=0.0	SMASS=-3

The additional tags in the column for every thermostat have to be set to the given values. Otherwise the NVE ensemble will not be realized. There are two implementations of the Nose-Hoover thermostat in VASP which will give the same results. The MDALGO=0 version can be used even if the code was compiled without the precompiler option -Dtbdyn. Other tags related to molecular-dynamics simulations can be found here.

An example INCAR file for the Andersen thermostat could look like

 #INCAR molecular-dynamics tags NVE ensemble 
 IBRION = 0                   # choose molecular-dynamics 
 MDALGO = 1                   # using Andersen thermostat
 ISIF = 2                     # 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 
 ANDERSEN_PROB = 0.0          # setting Andersen collision probability to zero to get NVE enseble

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.

@@ Line 1: / Line 1: @@
-The NVE ensemble is a statistical ensemble that is used to study material properties under the conditions of a constant particle number N, constant volume V and an internal energy E fluctuating around an equilibrium value E. This page describes how to sample the NVE ensemble from a [[Molecular dynamics calculations|molecular-dynamics]] run.
+The [[NVE ensemble]] (micro-canonical ensemble) is a [[:Category:Ensembles|statistical ensemble]] that is used to study material properties under the conditions of a constant particle number N, constant volume V and an internal energy E fluctuating around an equilibrium value E. This page describes how to sample the NVE ensemble from a [[Molecular dynamics calculations|molecular-dynamics]] run.
 ''' Instructions for setting up a NVE ensemble '''
-For the NVE ensemble there are two equivalent choices of thermostats to set up a [[Molecular dynamics calculations|molecular-dynamics]] run.
+There are two choices of thermostats which can be adjusted to set up a [[Molecular dynamics calculations|molecular-dynamics]] run.
-The user can either set the [[Andersen thermostat]] or the [[Nose-Hoover thermostat]] to give a NVE ensemble. The [[Andersen thermostat]] thermostat can be used by setting the collision probability ({{TAG|ANDERSEN_PROB}}) with the fictitious heat bath to zero and [[Nose-Hoover thermostat]] by setting the mass of the virtual degree to minus three. Both settings will switch the thermostat of such that the velocities
+The [[Andersen thermostat]] can be used by setting the collision probability ({{TAG|ANDERSEN_PROB}}) with the fictitious heat bath to zero and the  [[Nose-Hoover thermostat]] by setting the mass of the virtual degree to minus three. Both settings will switch the thermostat of such that the velocities are determined by the [[Hellmann-Feynman forces]] or [[Machine-learned force fields]] only.
-are determined by the [[Hellmann-Feynman forces]] or [[Machine-learned force fields]] only.
+See table for the corresponding MDALGO setting and related tags.
 {|class="wikitable" style="margin:aut
@@ Line 14: / Line 14: @@
 | additional tags  to set || style="text-align:center;"| {{TAG|ANDERSEN_PROB}}=0.0 ||style="text-align:center;"| {{TAG|SMASS}}=-3
 |}
 The additional tags in the column for every thermostat have to be set to the given values. Otherwise the NVE ensemble will not be realized.
 There are two implementations of the [[Nose-Hoover thermostat]] in VASP which will give the same results. The {{TAG|MDALGO}}=0 version can be used even if the code was compiled without the precompiler option [[Precompiler_options#-Dtbdyn|-Dtbdyn]].
 Other tags related to molecular-dynamics simulations can be found [[Molecular dynamics calculations|here]].
-''An example INCAR file for the [[Andersen thermostat]] could look like''
+''An example {{FILE|INCAR}} file for the [[Andersen thermostat]] could look like''
    #INCAR molecular-dynamics tags NVE ensemble
-   IBRION = 0                   # choose molecular-dynamics
+   {{TAGBL|IBRION}} = 0                   # choose molecular-dynamics
-   MDALGO = 1                   # using Andersen thermostat
+   {{TAGBL|MDALGO}} = 1                   # using Andersen thermostat
-   ISIF = 2                     # compute stress tensor but do not change box volume/shape
+   {{TAGBL|ISIF}} = 2                     # compute stress tensor but do not change box volume/shape
-   TEBEG = 300                  # set temperature
+   {{TAGBL|TEBEG}} = 300                  # set temperature
-   NSW = 10000                  # number of time steps
+   {{TAGBL|NSW}} = 10000                  # number of time steps
-   POTIM = 1.0                  # time step in femto seconds
+   {{TAGBL|POTIM}} = 1.0                  # time step in femto seconds
-   ANDERSEN_PROB = 0.0          # setting friction coefficient in inverse time units for two atom types
+   {{TAGBL|ANDERSEN_PROB}} = 0.0          # setting Andersen collision probability to zero to get NVE enseble
 {{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==
-{{FILE|REPORT}}, [[Molecular dynamics calculations]]
+[[Molecular dynamics calculations|Molecular-dynamics calculations]], {{TAG|ISIF}}, {{TAG|MDALGO}}, [[:Category:Ensembles|Ensembles]]
 [[Category:Molecular dynamics]][[Category:Ensembles]][[Category:Thermostats]]