Periodic-boundary conditions
Periodic-boundary conditions are indicated by use of the PBC
command. It can take the following options and directive
LATT_TYPE
The shape of the unit cell.CUBIC
: cubic unit cell,HEXAG
: hexagonal unit cell,PARAP
: a parallelpiped shaped cellBOXSIZE
For cubic unit cells this specifies the length of the side of the cube in Angstroms.HEXWIDTH, HEXHEIGHT
For hexagonal unit cells this specifies the width and height of the cell in Angstroms.VEC
A directive which should be followed by 3 numbers to specify a lattice vector. When specifying lattice vectors like this, there are usually 3 instances of such a directive and the vectors will be checked that they conform to the specifiedLATT_TYPE
. This is the only way to specify lattice vectors forLATT_TYPE=PARAP
. The program will not error if less than 3 vectors have been given, as in principle 1 or 2 dimensional periodicity could be desired, although this has not been implemented.
To define parallelpiped lattice vectors, something like the following would be used
{PBC,LATT\_TYPE='PARAP' VEC,1.0,0.0,0.0 VEC,0.0,1.5,1.5 VEC,0.0,0.0,1.5 }