BTCL Command Parameter Types

The BTCL parameter values themselves depend on the particular parameter to be assigned. There are five types of parameters:

real: takes any numeric value.
integer: takes any integer value (rounded down towards zero).
string: takes any character sequence up to a space or enclosed between a pair of quotes (" ") or braces ({ }).
enum: takes a string that may be only one of a list of allowed patterns. Enum values are case-insensitive and some can accept abbreviations.
Boolean: takes a string that maps to the values 1 or 0.
Values that map to 1 are TRUE, T, YES, Y, ON, and 1.
Values that map to 0 are FALSE, F, NO, N, OFF, and 0.
The value-strings read for Boolean types are case-insensitive.

With Boolean-type parameters, an acceptable shorthand for b_param = TRUE is +b_param and for b_param = FALSE is -b_param. Note that the mere presence of a Boolean parameter is not enough to set it to TRUE.

Some parameters can be fixed or dynamic-length arrays of these types. For arrays, a list of values is required, for example, the stress parameter of the dynamics command, which can be used to set the stress parameters sxx, syy, etc.:

dynamics temperature = 300 time = 500 stress = {0.5 0.5 0.5 0.0 0.0 0.0}

Some BTCL commands allow you to specify subcommands that are executed at specified instances from within a BTCL command. For example, assuming that a molecular system has already been set up:

BTCL > minimize iteration = 50 method = cascade newton method = bfgs \ 
   execute +before command = "echo hello from minimizer" \ 
   execute every = 2 command = "print output +energy_summary +nonbond_energy" \
   execute every = 5 command = "print archive +velocity" \
   execute +after command = "echo good-bye from minimizer"

This command would set up a minimization run using the cascade method with BFGS Newton minimization over a maximum of 50 iterations. In addition, ``hello from minimizer'' and ``good-bye from minimizer'' would be printed at the start and end of the minimization, respectively, with instantaneous energy summary and nonbond energy values being printed every other step and velocities written to an archive file (run_name.arc) every 5 steps.

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