Quantum Monte Carlo Techniques and Defects in Semiconductors
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The continuum variational and diffusion quantum Monte Carlo (VMC and DMC) techniques are stochastic methods for obtaining expectation values of many-body wavefunctions. These methods are capable of achieving very high accuracy, yet the scaling with system size is sufficiently favorable to allow applications to condensed-matter systems. Defects in semiconductors pose a variety of challenges to computational electronic-structure methods. As well as the large system sizes required, one is faced with calculating energy differences between rather disparate interatomic bonding configurations, and calculating excited state energies, sometimes including the energies of multiplets. Applications of VMC and DMC to defects in semiconductors are still in their infancy but, as I will describe, these methods possess features that make them well suited for addressing some important issues in the field. In this chapter I first discuss why we expect VMC and DMC calculations to be valuable in studying defects in semiconductors. I then review the techniques themselves, concentrating on the issues most pertinent to calculations for defects in solids. I describe recent applications to self-interstitial defects in crystalline silicon, the low-energy electronic states of the neutral vacancy in diamond, and the Schottky defect energy in magnesium oxide. The chapter ends with a perspective on the future of such studies.
Keywords71.10.-w 71.17.-m 71.23.-k 71.55.-i 63.20Mt
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