formpair.xm

来自「一个很好的分子动力学程序」· XM 代码 · 共 49 行

#######################################################################
#                                                                     #
#  Example:  Using FORMULA option with PAIR potential model           #
#                                                                     #
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#    The FORMULA option allows you to build up a potential table      #
#  by specifying the actual formula for your function, rather         #
#  than entering a table of values.                                   #
#     This example also demonstrates the use of the POTENTIAL EVAL    #
#  command available with the PAIR potential model.                   #
#                                                                     #
#######################################################################
#     The format of the potential command is                          #
#                                                                     #
#               POTENTIAL PAIR type1 type2 ntable r0 rn  FORMULA      #
#                                                                     #
#  where   type1  is the first  atom type of the pair potential       #
#          type2  is the second atom type of the pair potential       #
#          ntable is the number of entries in the potential table     #
#          r0     is the radius corresponding to the table beginning  #
#          rn     is the radius corresponding to the table end        #
#                                                                     #
#######################################################################
#
#
#  Choose pair potential model
#
POTENTIAL SET PAIR 2
#
#  Set parameters for "quartic" potential function
#
CALC Ro    = 1.67
CALC RC    = 3.40
CALC DEPTH = 1
#
#  Produce potential using formula for quartic potential
#
EUNIT erg
POTENTIAL PAIR  1 2   100  0  3.40  FORMULA 
   DEPTH * ( ( (R-Rc)/(Ro-Rc) )^4 - 2 * ( (R-Rc)/(Ro-Rc) )^2 )
#
#  Evaluate resulting potential
#
CALC r = 0
repeat 21
   POTENTIAL EVAL PAIR 1 2  0 r
   CALC r = r + 0.170
end