v3_scale(&temp2,&temp2,tmp*B*exp(-mu*d_jk)*f_c_jk*0.5);
v3_add(&(ai->f),&(ai->f),&temp2); /* -1 skipped in f_a calc ^ */
/* scaled with 0.5 ^ */
v3_scale(&temp2,&temp2,tmp*B*exp(-mu*d_jk)*f_c_jk*0.5);
v3_add(&(ai->f),&(ai->f),&temp2); /* -1 skipped in f_a calc ^ */
/* scaled with 0.5 ^ */