SMP (Shared Memory Parallelism) and DMP (Distributed Memory Parallelism) are two different ways to write and run the code in parallel. They both require special attention, especially when doing summation and I/O. Here the SMP build fails because you have not defined if sum_force is a private or shared variable. If you are not familiar with SMP or DMP programming, you will need to spend some time learning how to write parallel code before attempting to modify the source code.