[CP2K:327] other questions about the calculation error

[Teodoro Laino]

Chun-Min,
please have a look at

http://www.theochem.ruhr-uni-bochum.de/research/marx/marx.pdf
(this manuscript is about CPMD but other similar publications about  
other PW codes are fine as well)

to have an idea how g-vectors are treated/stored in PW calculations.
Regarding the other question about what of your two results is correct:
looking at your input file none of them is correct.

The keyword PERIODIC:
http://cp2k.berlios.de/input/ 
InputReference~__ROOT__~FORCE_EVAL~SUBSYS~CELL.html#PERIODIC

controls the PBC of the atoms and  therefore also the construction of  
the neighbor lists used in QS/FIST or other part
of the package, but not the periodicity of the electrostatics.
The presence of this keyword alone does NOT decouple the coupling  
between periodic replica due to the
treatment of the electrostatic with PW (have a look always at the  
manuscript of Hutter/Marx for details).

The correct input looks like (showing only modified sections):
&FORCE_EVAL
      [..]
     &MGRID
       CUTOFF 250
       # Use a larger cutoff
     &END MGRID
     [..]
     &POISSON
         PERIODIC NONE
         POISSON_SOLVER MT
         # no periodicity for the electrostatic. Decoupling achieved  
through the Martyna-Tuckerman Scheme..
     &END
     # (POISSON in http://cp2k.berlios.de/input/ 
InputReference~__ROOT__~FORCE_EVAL~DFT~POISSON.html)
   &END DFT
   [..]
&END FORCE_EVAL

IMPORTANT:
To be correct, the MT algorithm requires a computational box at least  
double the size of the dimensions of the molecule you
want to simulate. If the box is smaller than this value the result  
will not be correct.

Teo