Fixed-node diffusion Monte Carlo description of nitrogen defects in zinc oxide

Abstract

Using fixed-node diffusion Monte Carlo (FN-DMC), we evaluate the formation energies and charge transition levels of substitutional nitrogen defects in the wide band gap semiconductor zinc oxide. The use of a direct-solution, many-body approach inherently secures a good description of electronelectron interactions, achieving high accuracy without adjustable parameters. According to FN-DMC nitrogen is a deep acceptor with a charge transition level 1.0(3) eV above the valence band maximum when 72 atom supercells are used. This result falls on the lower end of typically reported hybrid density functional results for the same sized supercells, which range from 1.0 -1.8 eV. Further, residual finite size effects due to charged defect image interactions in the 72 atom supercells are estimated by supercell extrapolation within hybrid density functional theory. When the finite size correction is included, we obtain a deep acceptor at 1.6(3) eV. This result is in good agreement with recent experimental measurements. We also analyze the local compressibility of charge according to FN-DMC and common density functionals, and find that the use of hybrid functionals obtain compressibilities in better agreement with the many-body theory. Our work illustrates the application of the FN-DMC method to a challenging point defect problem, demonstrating that uncertainties and approximations can be well-controlled.

Structural, electronic, and magnetic properties of bulk and epitaxial LaCoO3 through diffusion Monte Carlo

“…However, the accuracy of DFT has not yet been sufficient to differentiate between the two mechanisms [4,7]. Projector methods [24], such as Diffusion Monte Carlo (DMC) [25,26], are shown to be the most accurate and practical methods to tackle the ground states of complex, highly correlated materials with a similar success in the excited states [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. Although it is computationally more expensive, DMC explicitly accounts for the antisymmetry of the many-body wave function and electron correlation, without using any empirical parameters [25,26,44,45].…”

Relative energies and electronic structures of CoO polymorphs through ab initio diffusion quantum Monte Carlo

“…Here, N is the number of electrons in the simulation. With recent advances in computational capabilities, DMC has already been applied to various properties in binary transition metal oxides such as FeO 39 , NiO 43,44 , MnO 12? , TiO 2 37,45,46 , Ti 4 O 7 47 , VO 2 48,49 and ZnO 37,50,51 . While Co dimers and Co-containing molecular complexes have been studied previously, to our knowledge, DMC has not yet been applied to study bulk Co oxides 52,53 .…”

Charge Density and Redox Potential of LiNiO2 Using Ab Initio Diffusion Quantum Monte Carlo

“…Therefore, DFT based methods have been largely utilized in periodic systems. In this approach the nodal surface is often optimized by either varying the U interaction parameter or the exact exchange ratio in the hybrid-DFT functionals [41,45,63,64]. Second, Jastrow parameters (correlation functions) are added to the guiding wavefunction and then optimized to further capture manybody correlations in the system.…”