Influence of the atom position restraints on the calculation of the surface stress/tension

GROMACS version: 2021.4-Ubuntu-2021.4-2
GROMACS modification: No

Hi everyone!

Does anyone have information on how the position restraints of atoms affect the calculation of the surface tension of a SAM on a metallic layer?
The case is quite specific, even general information already helps.

Any informative source, formula, explanation…anything helps currently. You can find a lot online, but unfortunately also a lot that does not really help.

Greetings and a good start in the week,
Konsti

Hi Konsti,

You can refer for the formula used for surface-tension coupling; this is the one that GROMACS utilizes to compute the surface tension from the virial:
https://manual.gromacs.org/current/reference-manual/algorithms/molecular-dynamics.html#pressure-coupling

When position restrains are used the virial contains the contribution of forces depending on absolute positions. In my experience this has produced meaningless values of surface tension, e.g. one may get negative numbers even for a stable solid-liquid interface.