fix ti/rs command
-Syntax
--fix ID group-ID ti/rs lambda_initial lambda_final t_switch t_equil keyword value ... --
-
-
- ID, group-ID are documented in fix command -
- ti/rs = style name of this fix command -
- lambda_initial/lambda_final = initial/final values of the coupling parameter -
- t_switch/t_equil = number of steps of the switching/equilibration procedure -
- keyword = function -
-function value = function-ID - function-ID = ID of the switching function (1, 2 or 3) --
Example:
-fix ref all ti/rs 50.0 2000 1000
-fix vf vacancy ti/rs 10.0 70000 50000 function 2
-Description
-This fix allows you to compute the free energy temperature dependence -by performing a thermodynamic integration procedure known as -Reversible Scaling (de Koning99, de Koning00a). The thermodynamic integration is performed -using the nonequilibrium method of Adiabatic Switching -(Watanabe, de Koning96).
-The forces on the atoms are dynamically scaled during the simulation, -the rescaling is done in the following manner:
-
-where F_int is the total force on the atoms due to the interatomic -potential and lambda is the coupling parameter of the thermodynamic -integration.
-The fix acts as follows: during the first t_equil steps after the -fix is defined the value of lambda is lambda_initial , this is the -period to equilibrate the system in the lambda = lambda_initial -state. After this the value of lambda changes continuously from -lambda_initial to lambda_final according to the function defined -using the keyword function (described below), this is done in -t_switch steps. Then comes the second equilibration period of -t_equil to equilibrate the system in the lambda = lambda_final -state. After that the switching back to the lambda = lambda_initial -state is done using t_switch timesteps and following the same -switching function. After this period the value of lambda is kept -equal to lambda_initial indefinitely or until a unfix -erase the fix.
-The description of thermodynamic integration in both directions is -done in de Koning00b, the main reason is to try to -eliminate the dissipated heat due to the nonequilibrium process.
-The function keyword allows the use of three different switching -rates. The option 1 results in a constant rescaling where the lambda -parameter changes at a constant rate during the switching time -according to the switching function
-
-where tau is the scaled time variable t/t_switch. This switching -function has the characteristic that the temperature scaling is faster -at temperatures closer to the final temperature of the procedure. The -option number 2 performs the switching at a rate defined by the -following switching function
-
-This switching function has the characteristic that the temperature -scaling occurs at a constant rate during all the procedure. The option -number 3 performs the switching at a rate defined by the following -switching function
-
-This switching function has the characteristic that the temperature -scaling is faster at temperatures closer to the initial temperature of -the procedure.
-An example script using this command is provided in the -examples/USER/misc/ti directory.
-Restart, fix_modify, output, run start/stop, minimize info:
-No information about this fix is written to binary restart files.
-This fix computes a global vector quantitie which can be accessed by -various output commands. The vector has -2 positions, the first one is the coupling parameter lambda and the -second one is the time derivative of lambda. The scalar and vector -values calculated by this fix are “extensive”.
-No parameter of this fix can be used with the start/stop keywords of -the run command.
-The forces due to this fix are imposed during an energy minimization, -invoked by the minimize command.
-Restrictions
-This command is part of the USER-MISC package. It is only enabled if -LAMMPS was built with those packages. See the Making LAMMPS section for more info.
-Default
-The keyword default is function = 1.
--
(de Koning 99) M. de Koning, A. Antonelli and S. Yip, Phys Rev Lett, 83, 3973 (1999).
-(Watanabe) M. Watanabe and W. P. Reinhardt, Phys Rev Lett, 65, 3301 (1990).
-(de Koning 96) M. de Koning and A. Antonelli, Phys Rev E, 53, 465 (1996).
-(de Koning 00a) M. de Koning, A. Antonelli and S. Yip, J Chem Phys, 115, 11025 (2000).
-(de Koning 00b) M. de Koning et al., Computing in Science & Engineering, 2, 88 (2000).
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