[QE-users] Case study: KPOINT and band parallelization in Quantum ESPRESSO

[pranav kumar]

I took a simple 32-atom supercell of aluminum. Here is the input:

control
    calculation='scf'
    restart_mode='from_scratch',
    pseudo_dir = '.'
    outdir=./tmp/,
    prefix='al'
    tprnfor = .true.
    tstress = .true.
    disk_io='none'
 /
 &system
    ibrav=  0, A=4.05, nat=  32, ntyp= 1, ecutwfc =60.0,
    occupations='smearing', smearing='marzari-vanderbilt', degauss=0.05
 /
 &electrons
    diagonalization='david'
    mixing_beta = 0.7
 /
CELL_PARAMETERS alat2 0 00 2 00 0 2

ATOMIC_SPECIES
 Al  26.98 Al.pbe-n-kjpaw_psl.1.0.0.UPF
ATOMIC_POSITIONS crystal
      Al 0.00000000        0.00000000        0.00000000
      Al 0.25000000        0.25000000        0.00000000
      Al 0.25000000        0.00000000        0.25000000
      Al 0.00000000        0.25000000        0.25000000
      Al 0.50000000        0.00000000        0.00000000
      Al 0.75000000        0.25000000        0.00000000
      Al 0.75000000        0.00000000        0.25000000
      Al 0.50000000        0.25000000        0.25000000
      Al 0.00000000        0.50000000        0.00000000
      Al 0.25000000        0.75000000        0.00000000
      Al 0.25000000        0.50000000        0.25000000
      Al 0.00000000        0.75000000        0.25000000
      Al 0.50000000        0.50000000        0.00000000
      Al 0.75000000        0.75000000        0.00000000
      Al 0.75000000        0.50000000        0.25000000
      Al 0.50000000        0.75000000        0.25000000
      Al 0.00000000        0.00000000        0.50000000
      Al 0.25000000        0.25000000        0.50000000
      Al 0.25000000        0.00000000        0.75000000
      Al 0.00000000        0.25000000        0.75000000
      Al 0.50000000        0.00000000        0.50000000
      Al 0.75000000        0.25000000        0.50000000
      Al 0.75000000        0.00000000        0.75000000
      Al 0.50000000        0.25000000        0.75000000
      Al 0.00000000        0.50000000        0.50000000
      Al 0.25000000        0.75000000        0.50000000
      Al 0.25000000        0.50000000        0.75000000
      Al 0.00000000        0.75000000        0.75000000
      Al 0.50000000        0.50000000        0.50000000
      Al 0.75000000        0.75000000        0.50000000
      Al 0.75000000        0.50000000        0.75000000
      Al 0.50000000        0.75000000        0.75000000
K_POINTS automatic11 11 11  0 0 0




Here, I am running on single node with 48 processor with different number
of nkand nb

For example :
mpiexec.hydra -np 48 /USERS/pranav/compilation/q-e-qe-6.8/bin/pw.x -in
al.scf.david.in -nk 3 -nb 4

In First study, I varied nk while fixed nb=1. Here is the result

*nk nb time(sec)* 1 1 2062 1 1633 1 1444 1 1386 1 1388 1 13112 1 141

In second run, I fixed nk at 3 and varied nb and Here is the result

*nk nb time(sec)* 3  1 1443  2 1813  4 2553  8 426

Why is run-time increasing with increase in nb in second run? I was hoping
for decreasing in trend.


*Note: QE v6. 8 is compiled with intel-oneapi and internal FFT library*

-- 

PRANAV KUMAR
 Research Scholar
IIT MADRAS (AM18D011)
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