Defect engineering in two-dimensional pentagonal PdTe₂: Tuning electronic, optical, and magnetic properties

Recently, the successful synthesis of the pentagonal form of PdTe$_{2}$ monolayer (\emph{p}-PdTe$_{2}$) was reported [Liu~\emph{et al.}, Nature Materials \textbf{23}, 1339 (2024)]. In this work, we present an extensive first-principles density-functional theory (DFT) based computational study of vacancies in this material. Our study covers the evolution of the electronic, optical, and magnetic properties of various defect configurations and compares those to the pristine monolayer (\emph{p}-PdTe$_{2}$). We find that V$_{Pd}$ (V$_{Te}$) is the most stable defect in the~\emph{p}-PdTe$_{2}$ monolayer in the Te-rich (Pd-rich) limit. The defects alter the electronic properties of the monolayer significantly, leading to changes in their magnetic and optical properties due to the emergence of midgap impurity states. The defect complex V$_{Pd+4Te}$ is found to induce spin-polarization in the system with a total magnetic moment of 1.87 $\mu_{B}$. The obtained low diffusion energy barriers of 1.13 eV (in-plane) and 0.063 eV (top-bottom) corresponding to V$_{Te}$ indicates its facile migration probability is higher in the top-bottom direction at room temperature, as revealed by AIMD simulations as well. In order to guide the experimentalists, we also simulated the scanning-tunneling microscope (STM) images corresponding to all the defect configurations. Moreover, we also computed the electron-beam energies required for creating mono-vacancies. In the optical absorption spectra of the defective configurations, finite peaks appear below the band edge that are unique to the respective defective configuration. We have also computed the excess polarizability of the defective configurations with respect to the pristine one and found that maximum changes occur in the infrared and visible regions, providing insights into the change in their optical response as compared to the pristine monolayer.