Nonperiodic Poisson solvers

[Jadzia]

Hi everyone, 

I am trying to simulate a system with an isolated molecule, therefore I 
need a non-periodic setup. I have read the previous posts about the topic, 
but there are a number of questions open. They are both for the wavelet and 
the MT Poisson solver. 

*1) System size*
My simulations will be quite long (both MM and QM) and due to the movement 
of the molecule, to my understanding it needs to be avoided that molecule 
leaves the box. Will it be fine if I set the box size to 1000 Angstrom or 
is this not recommended? 

*2) Periodic cells*
This question is closely related to question 1). If I set the Poisson 
solver to non-periodic, could one set the CELL to periodic, and thus solve 
the problem that the molecule leaves the box?

*3) Ewald methods*
Also closely related to question 1). If I set the box size to 1000, even 
with Ewald as Poisson solver the system should be effectively non-periodic 
due to the large distance, right? Would this be a plausible alternative to 
the MT or wavelet solvers?

*4) Mixed force evaluations*
In the case that I have a mixed force evaluation setup and use the Wavelet 
solver (see the config file below), do I need to include the 
&CENTER_COORDINATES section also in the mixed force eval section, or only 
in the real force evaluation section?

*5) MT solver for periodic systems*
Is the MT solver only for nonperiodic systems in CP2K, or does it also work 
for periodic systems? In the publication it is at least written it works 
for periodic systems and even with ewald/spme. 

Looking forward to hearing from you.

Best wishes,
Jadzia



&GLOBAL
  PROJECT system
  RUN_TYPE md
  PRINT_LEVEL medium
&END global
&MOTION
  &MD
    ENSEMBLE langevin
    &LANGEVIN 
      GAMMA [fs^-1] 1.0E-3                        # "Langevin" gamma (adapt 
for your system) 
    &END LANGEVIN
    STEPS 5000000
    TIMESTEP 0.5
    TEMPERATURE 300.0
  &END MD  
  &PRINT
    &TRAJECTORY on
      FORMAT pdb
      FILENAME =cp2k.out.trajectory.pdb
      &EACH
        MD 10
      &END EACH
    &END TRAJECTORY
&END MOTION
&MULTIPLE_FORCE_EVALS
   FORCE_EVAL_ORDER 2 3
   MULTIPLE_SUBSYS true
&END
&FORCE_EVAL
  STRESS_TENSOR analytical
  METHOD mixed
  &MIXED
    MIXING_TYPE genmix
    &GENERIC
      VARIABLES a b
      MIXING_FUNCTION a+b
    &END
    @include cp2k.in.mapping
  &END
  &SUBSYS
    &TOPOLOGY
      &CENTER_COORDINATES 
      &END 
      CONNECTIVITY off
      COORDINATE pdb
      COORD_FILE_NAME system.pdb
    &END TOPOLOGY
    &CELL
      PERIODIC NONE
      ABC 20 20 20 
    &END CELL
  &END SUBSYS
&END FORCE_EVAL
&FORCE_EVAL
  STRESS_TENSOR analytical
  METHOD fist
  &MM
    &FORCEFIELD
      PARM_FILE_NAME system1.prm
      PARMTYPE chm
      &SPLINE
        EMAX_SPLINE 100000
        RCUT_NB 12.
      &END
    &END FORCEFIELD    
    &POISSON
      POISSON_SOLVER WAVELET
      PERIODIC NONE
      &EWALD 
        EWALD_TYPE NONE 
      &END EWALD 
    &END POISSON
  &END MM
  &SUBSYS
    &CELL
      PERIODIC NONE
      ABC 20 20 20
    &END CELL
    &TOPOLOGY
      &CENTER_COORDINATES 
      &END 
      COORDINATE pdb
      COORD_FILE_NAME system1.pdb
      CONN_FILE_FORMAT psf
      CONN_FILE_NAME system1.psf
    &END TOPOLOGY
    @include cp2k.in.sub.kind.element.c36
  &END SUBSYS
&END FORCE_EVAL
&FORCE_EVAL
  STRESS_TENSOR analytical
  METHOD fist
  &MM
    &FORCEFIELD
      PARM_FILE_NAME system2.prm
      PARMTYPE chm
      &SPLINE
        EMAX_SPLINE 100000
        RCUT_NB 12.
      &END
    &END FORCEFIELD    
    &POISSON
      POISSON_SOLVER WAVELET
      PERIODIC NONE
      &EWALD 
        EWALD_TYPE NONE 
      &END EWALD 
    &END POISSON
  &END MM
  &SUBSYS
    &CELL
      PERIODIC NONE
      ABC 20 20 20
    &END CELL
    &TOPOLOGY
      &CENTER_COORDINATES 
      &END 
      COORDINATE pdb
      COORD_FILE_NAME system2.pdb
      CONN_FILE_FORMAT psf
      CONN_FILE_NAME system2.psf
    &END TOPOLOGY
    @include cp2k.in.sub.kind.element.c36
  &END SUBSYS
&END FORCE_EVAL

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