src/contrib/test.c

   1 /*
   2  *
   3  *                This source code is part of
   4  *
   5  *                 G   R   O   M   A   C   S
   6  *
   7  *          GROningen MAchine for Chemical Simulations
   8  *
   9  *                        VERSION 3.3.99_development_20071104
  10  * Written by David van der Spoel, Erik Lindahl, Berk Hess, and others.
  11  * Copyright (c) 1991-2000, University of Groningen, The Netherlands.
  12  * Copyright (c) 2001-2006, The GROMACS development team,
  13  * check out http://www.gromacs.org for more information.
  14
  15  * This program is free software; you can redistribute it and/or
  16  * modify it under the terms of the GNU General Public License
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  18  * of the License, or (at your option) any later version.
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  20  * If you want to redistribute modifications, please consider that
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  34  */
  35 #ifdef HAVE_CONFIG_H
  36 #include <config.h>
  37 #endif
  38
  39 #include <stdio.h>
  40 #include <math.h>
  41 #include "typedefs.h"
  42 #include "statutil.h"
  43 #include "copyrite.h"
  44 #include "gmx_fatal.h"
  45 #include "xvgr.h"
  46 #include "pdbio.h"
  47 #include "macros.h"
  48 #include "smalloc.h"
  49 #include "vec.h"
  50 #include "pbc.h"
  51 #include "physics.h"
  52 #include "names.h"
  53 #include "txtdump.h"
  54 #include "trnio.h"
  55 #include "symtab.h"
  56 #include "confio.h"
  57
  58 real pot(real x,real qq,real c6,real c12)
  59 {
  60   return c12*pow(x,-12)-c6*pow(x,-6)+qq*ONE_4PI_EPS0/x;
  61 }
  62
  63 real dpot(real x,real qq,real c6,real c12)
  64 {
  65   return -(12*c12*pow(x,-13)-6*c6*pow(x,-7)+qq*ONE_4PI_EPS0/sqr(x));
  66 }
  67
  68 int main(int argc,char *argv[])
  69 {
  70   static char *desc[] = {
  71     "Plot the potential"
  72   };
  73   static real c6=1.0e-3,c12=1.0e-6,qi=1,qj=2,sig=0.3,eps=1,sigfac=0.7;
  74   t_pargs pa[] = {
  75     { "-c6",   FALSE,  etREAL,  {&c6},  "c6"   },
  76     { "-c12",  FALSE,  etREAL,  {&c12}, "c12"  },
  77     { "-sig",  FALSE,  etREAL,  {&sig}, "sig"  },
  78     { "-eps",  FALSE,  etREAL,  {&eps}, "eps"  },
  79     { "-qi",   FALSE,  etREAL,  {&qi},  "qi"   },
  80     { "-qj",   FALSE,  etREAL,  {&qj},  "qj"   },
  81     { "-sigfac", FALSE, etREAL, {&sigfac}, "Factor in front of sigma for starting the plot" }
  82   };
  83   t_filenm fnm[] = {
  84     { efXVG, "-o", "potje", ffWRITE }
  85   };
  86 #define NFILE asize(fnm)
  87
  88   FILE      *fp;
  89   int       i;
  90   real      qq,x,oldx,minimum,mval,dp[2],pp[2];
  91   int       cur=0;
  92 #define next (1-cur)
  93
  94   /* CopyRight(stdout,argv[0]);*/
  95   parse_common_args(&argc,argv,PCA_CAN_VIEW,
  96                     NFILE,fnm,asize(pa),pa,asize(desc),
  97                     desc,0,NULL);
  98
  99   if (opt2parg_bSet("-sig",asize(pa),pa) ||
 100       opt2parg_bSet("-eps",asize(pa),pa)) {
 101     c6  = 4*eps*pow(sig,6);
 102     c12 = 4*eps*pow(sig,12);
 103   }
 104   else if ((c6 != 0) && (c12 != 0)) {
 105     sig = pow(c12/c6,1.0/6.0);
 106     eps = c6*c6/(4*c12);
 107   }
 108   else {
 109     sig = eps = 0;
 110   }
 111   printf("c6    = %12.5e, c12     = %12.5e\n",c6,c12);
 112   printf("sigma = %12.5f, epsilon = %12.5f\n",sig,eps);
 113   qq = qi*qj;
 114
 115   fp = xvgropen(ftp2fn(efXVG,NFILE,fnm),"Potential","r (nm)","E (kJ/mol)");
 116   if (sig == 0)
 117     sig=0.25;
 118   minimum = -1;
 119   mval    = 0;
 120   oldx    = 0;
 121   for(i=0; (i<100); i++) {
 122     x    = sigfac*sig+sig*i*0.02;
 123     dp[next] = dpot(x,qq,c6,c12);
 124     fprintf(fp,"%10g  %10g  %10g\n",x,pot(x,qq,c6,c12),
 125             dp[next]);
 126     if ((i > 0) && (dp[cur]*dp[next] < 0)) {
 127       minimum = oldx + dp[cur]*(x-oldx)/(dp[cur]-dp[next]);
 128       mval    = pot(minimum,qq,c6,c12);
 129       /*fprintf(stdout,"dp[cur] = %g, dp[next] = %g  oldx = %g, dx = %g\n",
 130         dp[cur],dp[next],oldx,x-oldx);*/
 131       printf("Minimum at r = %g (nm). Value = %g (kJ/mol)\n",
 132               minimum,mval);
 133     }
 134     cur = next;
 135     oldx = x;
 136
 137   }
 138   ffclose(fp);
 139
 140   do_view(ftp2fn(efXVG,NFILE,fnm),NULL);
 141
 142   thanx(stderr);
 143
 144   return 0;
 145 }
 146
 147