Speaker
Description
COMPUTATIONAL MODELLING STUDIES ON SCALING OF BULK AND SURFACES OF SPERRYLITE AND COOPERITE USING CASTEP AND ONETEP CODES
Thato Manyama, Peace Mkhonto and Phuti Ngoepe
University of Limpopo, Materials Modelling Centre, Private Bag x1106, Sovenga, 0727
e-mail address: thatosammuel50@gmail.com
Abstract
We have employed the CASTEP and ONETEP codes to investigate their scaling on the bulk and surfaces of sperrylite (PtAs2) and cooperite (PtS) models. The density functional theory dispersion correction (DFT-D) with generalized gradient approximation and the Perdew-Burke-Ernzerhof functional (GGA-PBE) using ultrasoft pseudopotential were employed within the CASTEP code. The van der Waals with the density functional (vdW-DF2) with norm-conserving pseudopotentials were adopted for the ONETEP codes. Note that ONETEP does not optimize the lattice; therefore the lattice parameters for the bulk structures were determined from CASTEP. The occupancy of the Pt d-orbital was corrected by Hubbard U-parameters. In CASTEP we have found that for bulk PtAs2 the U-parameter reduced the lattice parameters and closed the band gap of the model However, when we applied pressure to the PtAs2, the band gap opened as the pressure was increased, and a pressure of 5.00 GPa resulted in a lattice parameters of 5.964 Å and a band gap of 0.215 eV, which were in good agreement with experiments. In the case of PtS, we found that the U-parameters expanded the band gap to 0.845 eV, and the lattice was recreated to 3.469 Å and 6.143 Å using a pressure of 4.00 GPa. On the band gap determination, ONETEP made a similar observation. We observed that ONETEP has good scaling of the bulk model, particularly for huge supercells, demonstrating ONETEP's ability to manage large systems. For surface the same parameters were adopted and we found that ONETEP can handle large surface supercells with ease compared to CASTEP. This study demonstrated ONETEP's ability to handle huge systems as well as the models' performance with vdW dispersion correction.
Keywords: CASTEP code; ONETEP code; U-parameters; Pressure; Bulk structure; Surfaces
