# Open SourceMolecular Dynamics

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events:2018_summer_school:converging_cutoff

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# Converging the cutoff for a more difficult problem

### Input files

The complete set of files for this exercise can be found here.

This exercise is similar to the previous one, but uses a setup and system more typical of CP2K usage. We will use a system of 32 H2O water molecules within a periodic box. Here is the input template:

&GLOBAL
PRINT_LEVEL MEDIUM
PROJECT cuttoff-test
RUN_TYPE ENERGY_FORCE
&END GLOBAL

&FORCE_EVAL
METHOD Quickstep
&DFT
BASIS_SET_FILE_NAME BASIS_MOLOPT
POTENTIAL_FILE_NAME GTH_POTENTIALS
WFN_RESTART_FILE_NAME ../cuttoff-test-RESTART.wfn
CHARGE 0
MULTIPLICITY 1
&MGRID
NGRIDS 4
CUTOFF LT_cutoff
REL_CUTOFF LT_rel_cutoff
&END
&QS
EPS_DEFAULT 1.0E-12
METHOD GPW
&END

&SCF
SCF_GUESS RESTART
EPS_SCF 5.e-7
MAX_SCF 15
&OT
PRECONDITIONER FULL_ALL
MINIMIZER DIIS
&END OT
&OUTER_SCF
EPS_SCF 5.0E-7
MAX_SCF 1
&END OUTER_SCF
&END SCF

&XC
&XC_FUNCTIONAL PBE
&END XC_FUNCTIONAL
&XC_GRID
! defaults
XC_SMOOTH_RHO NONE
XC_DERIV PW
&END XC_GRID
&END XC

&END DFT
&SUBSYS
&CELL
ABC 9.8528 9.8528 9.8528
PERIODIC XYZ
&END CELL

&KIND H
BASIS_SET DZVP-MOLOPT-SR-GTH-q1
POTENTIAL GTH-PBE-q1
&END

&KIND O
BASIS_SET DZVP-MOLOPT-SR-GTH-q6
POTENTIAL GTH-PBE-q6
&END KIND

&TOPOLOGY
COORDINATE XYZ
COORD_FILE_NAME ../structure.xyz
CONNECTIVITY OFF
&END TOPOLOGY
&END SUBSYS

&PRINT
&FORCES
&END
&END
&END FORCE_EVAL


Compared to the Si example, this is a larger system, we are using the OT optimizer in a good setup for a small to medium insulating system:

    &SCF
SCF_GUESS RESTART
EPS_SCF 5.e-7
MAX_SCF 15
&OT
PRECONDITIONER FULL_ALL
MINIMIZER DIIS
&END OT
&OUTER_SCF
EPS_SCF 5.0E-7
MAX_SCF 1
&END OUTER_SCF
&END SCF

and we are also saving the forces on the atoms

  &PRINT
&FORCES
&END
&END

We save the forces as for many purposes (MD) converging the forces reasonably is more important than the total energy of the system.

The runcutoff file is a shell script as before to generate the different input files:

#!/bin/bash

cutoffs="100 200 300 400 500 600 700 800 900 1000 1100 1200"

template_file=input_template.inp
input_file=input.inp

rel_cutoff=60

for ii in $cutoffs ; do work_dir=cutoff_${ii}Ry
if [ ! -d $work_dir ] ; then mkdir$work_dir
else
rm -r $work_dir/* fi sed -e "s/LT_rel_cutoff/${rel_cutoff}/g" \
-e "s/LT_cutoff/${ii}/g" \$template_file > $work_dir/$input_file
done
remember to make it executable

### Running the system

When you run the shell script you should get a series of directories, cutoff_\${cutoff}Ry. Run the input files in each directory (you may want to setup a script to do this).

At the end you should have a set of output files that contain the total energy of the system and the forces on each atom.