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How to set up atomic geometries

Before an electronic structure calculation can be performed, it is necessary to specify a starting geometry for the atomic structure of the system we want to study. If this geometry is invariant under certain discrete crystallographic symmetry operations, the computational load can be reduced considerably by exploiting these symmetries. Therefore it is recommended to analyze the symmetry of the atomic geometry before starting the calculation, and to choose the unit cell in such a way that a maximum number of symmetries is met. The fhi98md code is distributed together with the fhi98start utility which helps to search for relevant symmetries and to set up crystals and slabs from some standard crystallographic symmetry classes.

Under UNIX environment, for example, the fhi98start utility is usually invoked by the same shell-script that runs fhi98md (below a protocol of the fhi98start run is saved in the file start.out):


#! /bin/csh -xvf
.....
set FHI98MD = ~/fhi98md
.....
cp ${FHI98MD}/fhimd/fhi98md .
cp ${FHI98MD}/start/fhi98start .
.....
######################################################
# run fhi98start program and build up  inp.ini       #
# - in principle one could create inp.ini by hand,   #
#   but fhi98start gives a consistent and optimized  #
#   input for fhi98md                                #
######################################################
./fhi98start | tee start.out

######################################################
#                   run fhi98md                      #
######################################################
./fhi98md
.....


next up previous contents index
Next: Choice of the k-point Up: Step-by-step description of calculational Previous: Step-by-step description of calculational
Matthias Wittenberg
1999-08-06