         return error;
         
     // run the kernel
-    gpu_nvt_step_two_kernel<<< grid, threads >>>(pdata, d_group_members, group_size, d_net_force, Xi, deltaT);
+    gpu_nvt_step_two_kernel<<< grid, threads >>>(pdata, d_group_members, group_size, Xi, deltaT);
     
     if (!g_gpu_error_checking)
         {

        {
        unsigned int idx = d_group_members[group_idx];
   
        // update positions to the next timestep and update velocities to the next half step
        float4 pos = tex1Dfetch(pdata_pos_tex, idx);
        // read in the net force and calculate the acceleration
        float4 accel = tex1Dfetch(net_force_tex, idx);
        float mass = tex1Dfetch(pdata_mass_tex, idx);

void gpu_nvt_step_two_kernel(gpu_pdata_arrays pdata,
                             unsigned int *d_group_members,
                             unsigned int group_size,
                             float Xi,
                             float deltaT)
    {
