[Pw_forum] questions about the calculation time

[Xinxin Yao]

Dear all,

  Recently I calculated a large supercell with 96 atoms and 400 valence electrons.
I found some strange phenomenons of calculation time. 

This is a part of the output file:

#    Self-consistent Calculation
#
#     iteration #  1     ecut=    30.00 Ry     beta=0.20
#     Davidson diagonalization with overlap          (about 5min)
#     ethr =  1.00E-05,  avg # of iterations = 12.2  (longer than 10min)
# 
#     total cpu time spent up to now is    440.62 secs
# 
#     total energy              = -3750.38793850 Ry
#     Harris-Foulkes estimate   = -3754.78120012 Ry
#     estimated scf accuracy    <    14.37337387 Ry

The diagonalization process takes a few time about 5 minutes, but after the line
"ethr =" appeares, until the next display of output file, it takes much long time
than the former diagonalization process, larger than 10 minutes. What cost so much
time in this process?

And the cpu time is less than the real time. Does it mean the cpu efficiency is
low? How could I improve the cpu efficiency?

Thank you!

Xinxin Yao