MPI parallel performance for parallelization on the layer loop (upper) and the load balance in the case of 8 MPI processes (lower). The white, gray, and black bars correspond, respectively, to the wall times for atomic lines, molecular lines, and continuum. The computation was performed, using gfortran 10.2 + Open MPI 4.1 + HDF5 1.12, on 2.3 GHz 8-Core Intel Core i9 processors.