boundary condition in classical potential

[chethankumar_m]

Hi all,
is it possible to impose boundary condition(periodic or aperiodic) in classical potential? Using DFT we can impose using Poisson solver. if it is possible in classical potential simulation please elaborate it.
Thank you

[Julian Schneider]

In the ATK-Classical calculator, the boundary conditions are periodic for BulkConfiguration and a vacuum-padded cell for MoleculeConfigurations.
If you want to switch off periodic boundary conditions for a bulk-configuration in certain directions, you can increase the length of the cell vector in this direction to add a vacuum padding, which is larger than the interaction range of the potential, so that one side of the configuration does not interact with the opposite side.

If you want to impose more specialized boundary conditions, which e.g. modify the forces on the atoms (e.g. walls), you can do this using a hook function.

[chethankumar_m]

Thank you Julian Schneider, is it the same case for device configuration?(calculation of phonon transmission spectrum)

[Julian Schneider]

The case of device configurations is a bit more tricky. For normal MD and Optimization calculations, the periodic boundary conditions are only active in x- and y-direction, whereas there is no PBC in z-direction.
For NEGF-phonon-transmisson calculations, however, the z-direction is semi-periodic (similar to a DFT-device), meaning that the periodicity on both sides is given by the periodic electrodes. In practice, this is achieved by adding the atoms of the electrodes on both sides to the central regions and using this extended system to calculate the dynamical matrix of the central region. The  dynamical matrices of the electrodes are calculated as regular 3D-periodic bulk configurations.