pair_style hybrid/overlay/mlml

Syntax

pair_style hybrid/overlay/mlml keyword value style1 args style2 args ...

  • keyword = zero

  • style1,style2 = list of one or more pair styles and their arguments

  • factor1,factor2 = scale factors for pair styles, may be a variable

  • zero or more keyword/value pairs may be appended

  • keyword = angmom or gjf or omega or scale or tally or zero

    zero value = no or yes
  no = do not set total pair_style force to zero
  yes = set total pair_style force to zero

Examples

pair_style hybrid/overlay/mlml lj/cut 5.0 pace
pair_coeff * * lj/cut 2 1.0 1.0
pair_coeff * * pace 1 Si.yace Si

pair_style hybrid/overlay/mlml lj/cut 5.0 uf3 3
pair_coeff * * lj/cut 2 1.0 1.0
pair_coeff * * uf3 1 W.uf3 W

pair_style hybrid/overlay/mlml pace pace table spline 5000 table spline 5000
pair_coeff * * pace 1 1 expensive_Si_ACE.yace Si
pair_coeff 1 1 table 1 1 expensive_Si_ACE_pairpot.table Si_Si
pair_coeff * * pace 2 2 cheap_Si_ACE.yace Si
pair_coeff 1 1 table 2 2 cheap_Si_ACE_pairpot.table Si_Si

Description

Warning

Bug Warning In the current version of LAMMPS, if a pair_style attempts to build a half neighbor list by pruning a full neighbor list created for a fix, it can result in all forces computed by that pair_style being zero (atoms effectively have no neighbors).

This issue affects ML-MIX in the following cases:

  • fix mlml is defined (which requires a full neighbor list).

  • All other pair_style definitions require half neighbor lists. (If at least one pair_style—such as ACE or UF3—requires a full neighbor list, then half neighbor lists are constructed correctly, and this issue does not occur.)

We are actively working to resolve this issue.

Warning

Pressure is not well defined In force-mixing, cell pressures are not well defined. LAMMPS will output pressure values, but (for now) these numbers are essentially meaningless. For this reason, you should not run NPT simulations.

This documentation should be considered as an extension to the documentation provided for the hybrid/overlay pair style. Everything that is valid for the hybrid/overlay pair style is also valid for the hybrid/overlay/mlml unless stated otherwise here.

The hybrid/overlay/mlml style is a variant of the hybrid/overlay style which allows for the use of multiple pair styles in one simulation. The hybrid/overlay/mlml style is part of the mlmix package. With the hybrid/overlay/mlml style, different pair styles can be evaluated in different spatial regions of the simulation domain. The full force vector is constructed through force-mixing, a method commonly used in QM/MM simulations.

The assignment of pair styles to type pairs is made via the pair_coeff command. For hybrid/overlay/mlml, an additional numeric argument must be specified after the sub-style name, which can either be 1 or 2. This value indicates the mlmix region to which the sub-style should be applied.

For hybrid/overlay/mlml, if a pair style is used multiple times in the pair_style command, the additional numeric argument to differentiate between the different instances of the sub-style must be specified after the number which indicates the mlmix region.

Forces from force mixing are not the derivatives of a potential energy function, subsequently the ‘total energy’ of the system is not well defined. Therefore, the hybrid/overlay/mlml will set global potential energy and virials to zero.

A consequence of force mixing is that the total force on the system may not be zero. To address this, the zero keyword can be used. If set to yes, the total force on the system will be modified such that the total is zero. This is achieved by averaging the net overall force on the system over all atoms and subtracting this from the force on each atom.

Acceleration

New in version 0.3.0

Warning

Kokkos acceleration for this pair_style is experimental and still in development. Some features may not work as expected, please report any issues you encounter.

This pair_style has a kokkos enabled version, which exists in order to allow ML/ML simulations to be performed using GPU accelerated kokkos pair_styles. Please see the restrictions section below for information on how the use of this differs from the CPU version.

The kokkos version of this pair_style will be automatically enabled if LAMMPS is launched with the kk suffix.

Restrictions

CPU Version: To use this pair_style, the i2_potential and d2_eval property/atoms must be defined. This pair_style is designed to be used in conjunction with the hybrid/overlay/mlml pair style.

GPU Version: new in version 0.3.0 To use this pair_style, the d_potential_1, d_potential_2, d_eval_1 and d_eval_2 property/atoms must be defined (for device compatibility).

As well as the restrictions that apply to the hybrid/overlay pair style, run_style respa is completely disabled for hybrid/overlay/mlml.

This fix is designed to be used in conjunction with the hybrid/overlay/mlml pair style.

This pair_style is designed to be used in conjunction with fix mlml. Please see fix mlml for more information.

Default

none