Quantum Monte Carlo study of high-pressure cubic TiO2

Abstract

We have studied the high-pressure cubic fluorite polymorph of TiO2 (c-TiO2) using the diffusion Monte Carlo (DMC) method. The estimated bulk modulus is within the range reported previously in density functional studies, high, but does not rival that of diamond. The calculated excitation energies within DMC are consistent with the results of GW approximation. The infrared frequency of c-TiO2, obtained via the frozen phonon method within DMC, shows non-negligible anharmonicity. This suggests that c-TiO2 might be stabilized if this anharmonicity is considered. Our DMC results could help to establish more accurate results for c-TiO2 compared with the widely-scattered mean-field results.

Structural stability and defect energetics of ZnO from diffusion quantum Monte Carlo

“…3.26 (16). Close agreement between DMC quasi-particle gap and experimental band gap have also been reported for MgO, 22 TiO 2 , 18 FeO, 101 MnO, 102 Based on the calculated cohesive energy of Zn and ZnO, the overall accuracy of our DMC calculations is ~0.3 eV. These errors, which are likely fixed-node errors, mostly cancel out for energy differences between similar systems.…”

“…For instance, DMC has recently been applied to study different properties of transition-metal oxides, 10,[16][17][18] MgSiO 3 perovskite, 19 boron-nitride, 20 and point defects in MgO, 21,22 Al, 23 Si [24][25][26] and diamond. 27 Other QMC methods have also recently been applied to study transition-metal oxides.…”

Hydrostatic and [001] Uniaxial Pressure on Anatase TiO2 by Periodic B3LYP-D* Calculations

“…The vibrational frequencies at the Γ point were computed within the harmonic approximation by diagonalizing the mass-weighted Hessian matrix. Details of the computational vibrational frequencies scheme can be found in refs 35 and 36 Electronic band structures were obtained at the appropriate high-symmetry path in the first Brillouin zone, 37 and the density of states (DOS) were calculated according to the Fourier−Legendre technique, with polynomial degree equal to 10.…”

Phase transitions and mechanical stability of TiO2 polymorphs under high pressure

“…We can see that these calculated results provide useful complementary data to experiments. Hence, cubic TiO 2 has been widely studied theoretically, including structural [40], elastic [40][41][42], electronic [51,52], optical [51], thermal [40,53,54] properties and phase transition [54,55].…”