PSTRESS: Difference between revisions

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{{TAGDEF|PSTRESS|[real]}}
{{TAGDEF|PSTRESS|[real]|0}}


Description: This tag controls whether Pulay corrections are added to the stress tensor or not. In molecular-dynamics calculations, it controls the pressure.
Description: Sets the external pressure in kB or adds corrections to the stress tensor.


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If the {{TAG|PSTRESS}} tag is specified VASP will add this pressure to the diagonals of the stress tensor and add an energy term <math> E= V * \mathrm{PSTRESS} </math> to the energy. This allows the user to converge to a specified external pressure.


{{TAG|PSTRESS}} can be also used to correct for errors caused by the Pulay stress, that is, errors in the calculated stress tensor caused by basis set incompleteness errors. In order to correct for the Pulay stress error, set {{TAG|PSTRESS}} to the negative value, that you obtain by calculating the pressure at a very large cutoff and the desired cutoff. Before using this tag in this way, please read the section {{TAG | Energy vs volume Volume relaxations and Pulay stress}}.
The unit of {{TAG|PSTRESS}} is kB.


In molecular-dynamics calculations within the {{TAG|NpT ensemble}} this tag controls the target pressure. The unit of {{TAG|PSTRESS}} is in kB.
During [[Ionic minimization|ionic minimization]], an energy term <math> E= V \times \mathrm{PSTRESS} </math> is added to the total energy and the value of  {{TAG|PSTRESS}} is subtracted from  the diagonals of the stress tensor. This allows to perform structure optimization at a specific external pressure.
 
In [[Molecular dynamics|molecular-dynamics calculations]] within the {{TAG|NpT ensemble}}, {{TAG|PSTRESS}} controls the target pressure for the Parinello-Rahman{{cite|parrinello:prl:1980}}{{cite|parrinello:jap:1981}} barostat.
 
Generally, if a negative value is supplied, the system is under effective tensile strain and during relaxations (or molecular dynamics simulations) the volume
will increase. If a positive value is supplied, the system is under compressive strain; this will decrease the volume during relaxations and molecular dynamics simulations.
 
{{TAG|PSTRESS}} can also be used to correct errors caused by the Pulay stress, i.e., errors in the calculated stress tensor caused by the incomplete plane wave basis set. To correct for Pulay-stress errors, set {{TAG|PSTRESS}} to the negative value of the Pulay stress. The Pulay stress is computed by taking the difference between the external pressure at the desired cutoff and a very large energy cutoff (check the  lines 'external pressure' in the {{TAG|OUTCAR}} file and calculate
pressure at cutoff you want to use <math> -  </math> pressure at large cutoff; this must be a negative value). Before using this tag in this manner, please read the following section carefully: {{TAG | Volume relaxation}}.


{{sc|PSTRESS|Examples|Examples that use this tag}}
{{sc|PSTRESS|Examples|Examples that use this tag}}

Latest revision as of 12:10, 19 August 2024

PSTRESS = [real]
Default: PSTRESS = 0 

Description: Sets the external pressure in kB or adds corrections to the stress tensor.


The unit of PSTRESS is kB.

During ionic minimization, an energy term is added to the total energy and the value of PSTRESS is subtracted from the diagonals of the stress tensor. This allows to perform structure optimization at a specific external pressure.

In molecular-dynamics calculations within the NpT ensemble, PSTRESS controls the target pressure for the Parinello-Rahman[1][2] barostat.

Generally, if a negative value is supplied, the system is under effective tensile strain and during relaxations (or molecular dynamics simulations) the volume will increase. If a positive value is supplied, the system is under compressive strain; this will decrease the volume during relaxations and molecular dynamics simulations.

PSTRESS can also be used to correct errors caused by the Pulay stress, i.e., errors in the calculated stress tensor caused by the incomplete plane wave basis set. To correct for Pulay-stress errors, set PSTRESS to the negative value of the Pulay stress. The Pulay stress is computed by taking the difference between the external pressure at the desired cutoff and a very large energy cutoff (check the lines 'external pressure' in the OUTCAR file and calculate pressure at cutoff you want to use pressure at large cutoff; this must be a negative value). Before using this tag in this manner, please read the following section carefully: Volume relaxation.

Examples that use this tag