First-principles calculation of monolayer PdSe2 with Se and Pd vacancy and its effect on quantum capacitance

Abstract

The emergence of 2-D materials such as graphene has caught the attention of the scientific community. 2-D materials have a higher surface area per unit mass, which is ideal for electrodes. Another popular material among researchers is the monolayer palladium diselenide or PdSe2, a semiconductor with a tunable bandgap energy. Since there are fewer states in the fermi level of PdSe2, the quantization effect is more prevalent, hence, it would most likely draw its capacitance from its electronic configuration. In this study, the electronic properties such as band structure, density of states, and quantum capacitance of pristine monolayer PdSe2, PdSe2 with Se, and Pd vacancy were calculated based on density functional theory via Quantum Espresso. The formation energies of all systems were energetically favourable. The system with Se vacancy has the highest formation energy with a value of -3.47 eV. The density of states of all systems were observed to have a local minima at the fermi level. More occupiable states around the valence band were observed for the systems with vacancy. Bader charge analysis showed a notable decrease of charge in Se atoms near the Pd vacancy, while the Pd atoms in the Se vacated system showed stronger charge transfer between Pd and another Se atom. The quantum capacitance and surface charge values were calculated using the density of states. Higher surface charge values at the negative voltage were observed for the systems with induced vacancies. Based on the results, the systems with vacancies have improved the quantum capacitance and surface charge at the negative potential.