[CPMD-list] CPMD/GROMOS96 quantum box sizes

[Ian R. Greig]

Dear CPMD-users,

I am trying to set up a small molecule-in-water simulation using the 
CPMD/GROMOS96 code of Roethlisberger et al. The small molecule is to be 
QM and the surrounding solvent MM. My starting coordinates have been 
generated using GROMOS96.

I have successfully performed a wavefunction optmization and a geometry 
optimization using a minimally sized quantum cell (obtained by fiddling 
with the cell parameters until I do not get the...

 WARNING!!!  Box too small in x direction
 WARNING!!!  Box too small in y direction
 WARNING!!!  Box too small in z direction

...messages in the output file.

When I use the geometry optimized structure as a restart point for the MD 
run I start to get the `box too small` warning messages at each MD step.

I have tried to increase the box size by upto 10 angstrom in all three 
dimensions and I still get the warning messages when I try to start the MD 
run (which procedes smoothly otherwise).

My input file can be found below.

Any thoughts would be greatly appreciated.

Ian


! MD startup run
! Oxazolinium ion in box of 55 water molecules
! A minimum quantum box is used for this run

&QMMM
TOPOLOGY
topol.gr
COORDINATES
coord.gr
INPUT
input.gr
LONG RANGE ELECTROSTATIC COUPLING
RCUT_NN
8.0
RCUT_MIX
8.0
RCUT_ESP
8.0
SPLIT
SAMPLE_INTERACTING
10
GROMOS
ADD_HYDROGEN
7
1 3 7 8 11 14 16
&END

&CPMD
QMMM
RESTART WAVEFUNCTION COORDINATES
MOLECULAR DYNAMICS
TEMPCONTROL IONS
341.0 30.0
MAXSTEP
200
TRAJECTORY SAMPLE
20
TIMESTEP
4.0
EMASS
600.0
MEMORY BIG
CONVERGENCE
1.0E-5  1.0E-4
SPLINE POINTS
3000
&END

&SYSTEM
ANGSTROM
POISSON TUCKERMAN
SYMMETRY
0
CELL
18.6  0.918  0.789  0  0  0
CUTOFF
70
CHARGE
+1
&END

&ATOMS
*H_GIA_BLYP KLEINMAN-BYLANDER
LMAX=S
4
5 10 13 18
*H_GIA_BLYP KLEINMAN-BYLANDER ADD_H
LMAX=S
10
*N_MT_GIA_BLYP KLEINMAN-BYLANDER
LMAX=P
1
4
*C_MT_GIA_BLYP KLEINMAN-BYLANDER
LMAX=P
8
1 3 6 7 8 11 14 16
*O_MT_GIA_BLYP KLEINMAN-BYLANDER
LMAX=P
5
2 9 12 15 17
&END

&DFT
NEWCODE
EXCHANGE CORRELATION TABLE NO
FUNCTIONAL BLYP
GC-CUTOFF
5.0E-06
&END





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                          Ian R. Greig

Chemistry Department                   Room 209, Green College
Room E257 2036 Main Mall               6201 Cecil Green Park Road
Vancouver, British Columbia            Vancouver, British Columbia
CANADA V6T 1Z1                         CANADA V6T 1Z1
Tel: + 1 604 822 4626                  Tel: + 1 604 221 1971
Fax: + 1 604 822 2847

irg20 at cantab.net
irg20 at chem.ubc.ca
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