n = 1;
     while(n <= Nc){
        fscanf(voisins,"%d%d%f%f%f%f",&i,&j,&r[0],&r[1],&r[2],&d);
        V = 0.0;E = 0.0;F = 0.0;
        for(p = 0;p < 3;p++){
           V += (D/pow(d,3.0))*(spin[3*i-3+p]-w[p])*spin[3*j-3+p];
           E += (spin[3*i-3+p]-w[p])*r[p];
           F += spin[3*j-3+p]*r[p];
        }
        G = -3*(D/pow(d,5.0))*E*F;
        dU += (V+G);
        n++;
     }