LATTICE CONSTRAINTS: Difference between revisions

Revision as of 09:18, 8 April 2022

LATTICE_CONSTRAINTS = [logical][logical][logical]

Description: The tag LATTICE_CONSTRAINTS determines whether the lattice dynamics are released (LATTICE_CONSTRAINTS=.TRUE.) in the given directions in molecular-dynamics calculations (IBRION=0).

This tag requires three boolean values for the $a$ , $b$ and $c$ direction of the lattice constants, respectively. By setting .TRUE. the lattice constant in the respective direction is allowed to change.

We recommend using LATTICE_CONSTRAINTS for (orthorombic) liquids in the isobaric-isothermal (NpT) ensemble in the following way:

LATTICE_CONSTRAINTS = .FALSE. .FALSE. .TRUE.

This way the first two lattice constants are not allowed to change. The third lattice constant needs to be free to change to allow volume changes for the barostat (the system is then like a piston). The constraints are necessary for liquids in NpT simulations, because if all lattice degrees of freedom are allowed to relax, irreversible deformations of the cell are very likely to happen that can lead to undesirable results.

Warning: LATTICE_CONSTRAINTS is only available for molecular-dynamics calculations.

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 This way the first two lattice constants are not allowed to change. The third lattice constant needs to be free to change to allow volume changes for the barostat (the system is then like a piston). The constraints are necessary for liquids in [[NpT ensemble|NpT]] simulations, because if all lattice degrees of freedom are allowed to relax, irreversible deformations of the cell are very likely to happen that can lead to undesirable results.
-{{NB|warning|This tag is only available for molecular-dynamics calculations.}}
+{{NB|warning|{{TAG|LATTICE_CONSTRAINTS}} is only available for molecular-dynamics calculations.}}
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