Estudo da estrutura eletrônica do sistema MgMoO4 via DFT

Abstract

This work studied the structure and electrical properties of magnesium molybdate in the monoclinic phase(MgMoO4) and triclinic phase(MgMoO4.H2O) . These materials are semiconductors with various applications, such as tunable lasers, hydrogen batteries, and electronic optical devices. To comprehend these properties, a theoretical analysis was proposed, utilizing Density Functional Theory (DFT) and the computational package CRYSTAL17. The use of DFT is a powerful alternative for describing the electrical and structural properties of crystalline solid materials, together with functionals that offer approximations to solve the interactions of many bodies. The functionals used in this work are the pure PBE and the hybrid functionals that result in higher computational costs but better results, such as B3LYP and HSE. Furthermore, the D3 Grimme approximation was used in conjunction with B3LYP, considering dispersion interactions. The calculations were performed, obtaining band structure, band gap, density of states, and Raman spectra. The band structure illustrated how the transition between the valence band and the conduction band occurs. In the monoclinic phase, this transition was indirect between the k points of the reciprocal lattice, Y − Γ, except for PBE, which showed a direct transition between the points Γ − Γ. The band gap value closest to the experimental result was calculated with B3LYP-D3, at a value of 5.4 eV. This was the first indication that this hybrid functional, in combination with the dispersion approximation, yielded better performance in the material calculations. For the triclinic phase, the band gap value was 5.92 eV for B3LYP-D3, and the transition was indirect between the k points of the reciprocal lattice, U − V . Hybrid functionals exhibited some fluctuations around this value, while PBE resulted in 4.01 eV. Except for the PBE, all functionals presented an indirect transition between the points Γ − V . The density of states showed that the contribution at the top of the valence band for both phases came from the oxygen p orbital, while in the conduction band, it was predominantly from the Mo d orbital, with some contribution from the oxygen p orbitals. The Raman provided detailed insight into the vibrational modes in the MgMoO4 structure, demonstrating better performance of B3LYP-D3 compared to experimental studies.