Why is that increasing the number of cores (openMP) in a computation does not decrease the duration of the process? Is it due to consecutive approximation?
I took a very simple system of Cu in FCC lattice and did the self consistent field (SCF) calculations with increasing number of cores. If you see the plot, the duration of task (Wall Clock) is nearly same or increases slightly. I am using an ordinary laptop with Intel Core i5 8th Generation, which has 4 cores (8 logical). Compiler: gfortran with openMP.
|No of Cores||CPU Clock (s)||Wall Clock (s)|