src/contrib/sigeps.c

   1 /*
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   4  *                This source code is part of
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   8  *          GROningen MAchine for Chemical Simulations
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  10  *                        VERSION 3.1
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  12  * This program is free software; you can redistribute it and/or
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  32
  33 #include <stdio.h>
  34 #include <math.h>
  35 #include "typedefs.h"
  36 #include "statutil.h"
  37 #include "copyrite.h"
  38 #include "fatal.h"
  39 #include "xvgr.h"
  40 #include "pdbio.h"
  41 #include "macros.h"
  42 #include "smalloc.h"
  43 #include "vec.h"
  44 #include "pbc.h"
  45 #include "physics.h"
  46 #include "names.h"
  47 #include "txtdump.h"
  48 #include "trnio.h"
  49 #include "symtab.h"
  50 #include "confio.h"
  51
  52 real pot(real x,real qq,real c6,real c12)
  53 {
  54   return c12*pow(x,-12)-c6*pow(x,-6)+qq*ONE_4PI_EPS0/x;
  55 }
  56
  57 real dpot(real x,real qq,real c6,real c12)
  58 {
  59   return -(12*c12*pow(x,-13)-6*c6*pow(x,-7)+qq*ONE_4PI_EPS0/sqr(x));
  60 }
  61
  62 int main(int argc,char *argv[])
  63 {
  64   static char *desc[] = {
  65     "Plot the potential"
  66   };
  67   static real c6=1.0e-3,c12=1.0e-6,qi=1,qj=2,sig=0.3,eps=1,sigfac=0.7;
  68   t_pargs pa[] = {
  69     { "-c6",   FALSE,  etREAL,  {&c6},  "c6"   },
  70     { "-c12",  FALSE,  etREAL,  {&c12}, "c12"  },
  71     { "-sig",  FALSE,  etREAL,  {&sig}, "sig"  },
  72     { "-eps",  FALSE,  etREAL,  {&eps}, "eps"  },
  73     { "-qi",   FALSE,  etREAL,  {&qi},  "qi"   },
  74     { "-qj",   FALSE,  etREAL,  {&qj},  "qj"   },
  75     { "-sigfac", FALSE, etREAL, {&sigfac}, "Factor in front of sigma for starting the plot" }
  76   };
  77   t_filenm fnm[] = {
  78     { efXVG, "-o", "potje", ffWRITE }
  79   };
  80 #define NFILE asize(fnm)
  81
  82   FILE      *fp;
  83   int       i;
  84   real      qq,x,oldx,minimum,mval,dp[2],pp[2];
  85   int       cur=0;
  86 #define next (1-cur)
  87
  88   /* CopyRight(stdout,argv[0]);*/
  89   parse_common_args(&argc,argv,PCA_CAN_VIEW,
  90                     NFILE,fnm,asize(pa),pa,asize(desc),
  91                     desc,0,NULL);
  92
  93   if (opt2parg_bSet("-sig",asize(pa),pa) ||
  94       opt2parg_bSet("-eps",asize(pa),pa)) {
  95     c6  = 4*eps*pow(sig,6);
  96     c12 = 4*eps*pow(sig,12);
  97   }
  98   else if ((c6 != 0) && (c12 != 0)) {
  99     sig = pow(c12/c6,1.0/6.0);
 100     eps = c6*c6/(4*c12);
 101   }
 102   else {
 103     sig = eps = 0;
 104   }
 105   printf("c6    = %12.5e, c12     = %12.5e\n",c6,c12);
 106   printf("sigma = %12.5f, epsilon = %12.5f\n",sig,eps);
 107   qq = qi*qj;
 108
 109   fp = xvgropen(ftp2fn(efXVG,NFILE,fnm),"Potential","r (nm)","E (kJ/mol)");
 110   if (sig == 0)
 111     sig=0.25;
 112   minimum = -1;
 113   mval    = 0;
 114   oldx    = 0;
 115   for(i=0; (i<100); i++) {
 116     x    = sigfac*sig+sig*i*0.02;
 117     dp[next] = dpot(x,qq,c6,c12);
 118     fprintf(fp,"%10g  %10g  %10g\n",x,pot(x,qq,c6,c12),
 119             dp[next]);
 120     if ((i > 0) && (dp[cur]*dp[next] < 0)) {
 121       minimum = oldx + dp[cur]*(x-oldx)/(dp[cur]-dp[next]);
 122       mval    = pot(minimum,qq,c6,c12);
 123       /*fprintf(stdout,"dp[cur] = %g, dp[next] = %g  oldx = %g, dx = %g\n",
 124         dp[cur],dp[next],oldx,x-oldx);*/
 125       printf("Minimum at r = %g (nm). Value = %g (kJ/mol)\n",
 126               minimum,mval);
 127     }
 128     cur = next;
 129     oldx = x;
 130
 131   }
 132   fclose(fp);
 133
 134   do_view(ftp2fn(efXVG,NFILE,fnm),NULL);
 135
 136   thanx(stderr);
 137
 138   return 0;
 139 }
 140
 141