Hi,

As we know, there is a parameter compressibility when using Pressure coupling command in Gromacs.

Is there a similar parameter in LAMMPS? How can I map this parameter to that of LAMMPS?

Thanks in advance.

GROMACS note:

Pressure coupling

- #### pcoupl:
**no**- No pressure coupling. This means a fixed box size.
**berendsen**- Exponential relaxation pressure coupling with time constant
**tau_p**[ps]. The box is scaled every timestep. It has been argued that this does not yield a correct thermodynamic ensemble, but it is the most efficient way to scale a box at the beginning of a run. **Parrinello-Rahman**- Extended-ensemble pressure coupling where the box vectors are subject to an equation of motion. The equation of motion for the atoms is coupled to this. No instantaneous scaling takes place. As for Nose-Hoover temperature coupling the time constant
**tau_p**[ps] is the period of pressure fluctuations at equilibrium. This is probably a better method when you want to apply pressure scaling during data collection, but beware that you can get very large oscillations if you are starting from a different pressure.

- #### pcoupltype:
**isotropic**- Isotropic pressure coupling with time constant
**tau_p**[ps]. The compressibility and reference pressure are set with**compressibility**[bar^{-1}] and**ref_p**[bar], one value is needed. **semiisotropic**- Pressure coupling which is isotropic in the x and y direction, but different in the z direction. This can be useful for membrane simulations. 2 values are needed for x/y and z directions respectively.
**anisotropic**- Idem, but 6 values are needed for xx, yy, zz, xy/yx, xz/zx and yz/zy components respectively. When the off-diagonal compressibilities are set to zero, a rectangular box will stay rectangular. Beware that anisotropic scaling can lead to extreme deformation of the simulation box.
**surface-tension**- Surface tension coupling for surfaces parallel to the xy-plane. Uses normal pressure coupling for the z-direction, while the surface tension is coupled to the x/y dimensions of the box. The first
**ref_p**value is the reference surface tension times the number of surfaces [bar nm], the second value is the reference z-pressure [bar]. The two**compressibility**[bar^{-1}] values are the compressibility in the x/y and z direction respectively. The value for the z-compressibility should be reasonably accurate since it influences the convergence of the surface-tension, it can also be set to zero to have a box with constant height.

^{-1}]

^{-1}) For water at 1 atm and 300 K the compressibility is 4.5e-5 [bar

^{-1}].

**no**

**all**

**com**