added old tangent to fix_neb for AGNI potential

            tangent[i][0] = vmax*delxn + vmin*delxp;

            tangent[i][1] = vmax*delyn + vmin*delyp;

            tangent[i][2] = vmax*delzn + vmin*delzp;

          } else {

          } else if(vnext < vprev) {

            tangent[i][0] = vmin*delxn + vmax*delxp;

            tangent[i][1] = vmin*delyn + vmax*delyp;

            tangent[i][2] = vmin*delzn + vmax*delzp;

          } else { //AGNI "old-tangent" method

            tangent[i][0] = delxn + delxp;

            tangent[i][1] = delyn + delyp;

            tangent[i][2] = delzn + delzp;

          }

        }