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fix vibmode command


fix ID vibmode 


fix 1 vibmode 


Enable multiple vibrational energy levels, defined on a per-species basis, to be used in a simulation. This fix is meant to be used with the collide_modify vibrate discrete setting which means that the vibrational energy of each (non-monoatomic) particle is discretized across one or more energy modes, each with its own characteristic vibrational temperature. This fix allocates per-particle storage for the mode indices and also has code to populate the multiple levels appropriately when particles are created. Collisions between pairs of particles will then transfer energy between the different modes of the two particles.

An overview of how to run simulations with multiple vibrational energy modes is given in the Section 4.12. This includes use of the species command with its vibfile option, and the use of the collide_modify vibrate discrete command. The section also lists all the commands that can be used in an input script to invoke various options associated with the vibrational energy modes. All of them depend on this fix vibmode command being defined.

Internally, this fix defines a custom particle attribute named "vibmode". It is an integer array with N values per particle. N is the maximum number of energy modes for any species defined in the simulation. The number of energy modes is half the vibrational degrees of freedom defined for each species. See the "species" command for how the degrees of freedom and associated vibrational temperatures and other properties are defined for each mode for each species.

Each of the N values is an integer count for the

Restart, output info:

No information about this fix is written to binary restart files.

However, the values of the custom particle attribute defined by this fix are written to the restart file. Namely the integer values stored in "vibmode" for each particle. As explained on the read_restart doc page these values can be re-assigned to particles when a restart file is read, if a new fix vibmode command is specified in the restart script before the first run command is used.

No global or per-particle or per-grid quantities are stored by this fix for access by various output commands.

However, the custom particle attributes defined by this fix can be accessed by the dump particle command, as p_vibmode. That means those per-particle values can be written to particle dump files.


This fix is required if "collide_modify vibrate discrete" is used and there is one or more species defined which haave multiple vibrational energy modes (2 or more). In this scenario, if it is not defined, an error will occur when a "create_particles" or run command is issued. Conversely, if no species has multiple vibrational modes, this fix cannot be used.

Defining this fix after particles have been created will not populate the vibrational energy modes of particles that already exist. An exception is if the read_restart command is used to read in particles from a previous simulation where this fix was used. In that case, defining this fix after reading the restart file will enable the particles to keep their previous vibrational energy mode values.

Related commands:

collide_modify vibrate discrete

Default: none