lots of mostly small changes ...

[physik/posic.git] / moldyn.c

diff --git a/moldyn.c b/moldyn.c
index 0fd1aca..db575e9 100644 (file)
--- a/moldyn.c
+++ b/moldyn.c
@@ -547,7 +547,7 @@ double potential_lennard_jones(t_moldyn *moldyn) {
        params=moldyn->pot_params;
        atom=moldyn->atom;
        count=moldyn->count;
-       eps=params->epsilon;
+       eps=params->epsilon4;
        sig6=params->sigma6;
        sig12=params->sigma12;
 
@@ -559,7 +559,7 @@ double potential_lennard_jones(t_moldyn *moldyn) {
                        help=d*d;                               /* 1/r^4 */
                        help*=d;                                /* 1/r^6 */
                        d=help*help;                            /* 1/r^12 */
-                       u+=eps*(sig12*d-sig6*help);
+                       u+=eps*(sig6*help-sig12*d);
                }
        }
        
@@ -579,7 +579,7 @@ int force_lennard_jones(t_moldyn *moldyn) {
        atom=moldyn->atom;      
        count=moldyn->count;
        params=moldyn->pot_params;
-       eps=params->epsilon;
+       eps=params->epsilon4;
        sig6=params->sigma6;
        sig12=params->sigma12;
 
@@ -598,11 +598,13 @@ int force_lennard_jones(t_moldyn *moldyn) {
                                h1*=h2;                         /* 1/r^14 */
                                h1*=sig12;
                                h2*=sig6;
-                               d=12.0*h1-6.0*h2;
+                               /* actually there would be a '-',       *
+                                * but f=-d/dr potential                */
+                               d=-12.0*h1+6.0*h2;
                                d*=eps;
                                v3_scale(&force,&distance,d);
-                               v3_add(&(atom[j].f),&(atom[j].f),&force);
-                               v3_sub(&(atom[i].f),&(atom[i].f),&force);
+                               v3_add(&(atom[i].f),&(atom[i].f),&force);
+                               v3_sub(&(atom[j].f),&(atom[j].f),&force);
                        }
                }
        }