other questions about the calculation error

[chun]

Teo,
    Thank you very much for your reply last time. I have other more
questions. Hopfully, you can enlighten me.
    I used cp2k to calculate one water molecule at the center of a
unit cell without periodic boundary condition (PBC NONE). If I change
the size of the unit cell (ABC) from 9.4 Angstrom cubic to 5.4
Angstrom cubic, the two results are different. After I checked the
output files, I found cp2k used two different sets of ' max spherical
cutoff ' in PW_GRID.

First of all, what is the ' max spherical cutoff ' ? Why is there
spherical cutoff in PW_GRID (planewave grid?) ?

Secondly, why is the ' max spherical cutoff ' changed for the
different size of the unit cell ?

Thirdly, which one is more reliable? the small unit cell or the large
one?


Thanks

Chun-Min



&FORCE_EVAL
  METHOD Quickstep
  &DFT
    BASIS_SET_FILE_NAME ~/cp2k/tests/QS/ALL_BASIS_SETS
    POTENTIAL_FILE_NAME ~/cp2k/tests/QS/POTENTIAL
    &MGRID
      CUTOFF 158
    &END MGRID
    &QS
      METHOD GAPW
      FULL_GAPW
    &END QS
    &SCF
      SCF_GUESS ATOMIC
    &END SCF
    &XC
      &XC_FUNCTIONAL BLYP
      &END XC_FUNCTIONAL
    &END XC
  &END DFT
  &SUBSYS
    &CELL
      ABC 9.4 9.4 9.4
#      ABC 5.4 5.4 5.4
      UNIT ANGSTROM
      PERIODIC NONE
    &END CELL
    &COORD
    O   4.700000    4.700000    4.634413
    H   4.700000    3.942864    5.220545
    H   4.700000    5.457136    5.220545
#    O   2.700000    2.700000    2.634413
#    H   2.700000    1.942864    3.220545
#    H   2.700000    3.457136    3.220545
    &END COORD
    &KIND H
      BASIS_SET 6-31G*
      POTENTIAL ALL
    &END KIND
    &KIND O
      BASIS_SET 6-31G*
      POTENTIAL ALL
    &END KIND
  &END SUBSYS
&END FORCE_EVAL
&GLOBAL
  PROJECT H2O
  PRINT_LEVEL MEDIUM
&END GLOBAL