Malliga Suewattana

Phaseless auxiliary-field quantum Monte Carlo calculations with plane waves and pseudopotentials : Applications to atoms and molecules

The phaseless auxiliary-field quantum Monte Carlo (AF QMC) method [S. Zhang and H. Krakauer, Phys. Rev. Lett. 90, 136401 (2003)] is used to carry out a systematic study of the dissociation and ionization energies of second-row group 3A\char21{}7A atoms and dimers: Al, Si, P, S, and Cl. In addition, the

Quantum simulations of realistic systems by auxiliary fields

{\mathrm{P}}_{2}

Kinetic Monte Carlo Simulations of Crystal Growth in Ferroelectric materials

dimer is compared to the third-row

Erratum: Crystal structure and cation off-centering in Bi(Mg1/2Ti1/2)O3[Phys. Rev. B86, 064105 (2012)]

{\mathrm{As}}_{2}

Electronic structure of lead pyrophosphate

dimer, which is also triply bonded. This method projects the many-body ground state by means of importance-sampled random walks in the space of Slater determinants. The Monte Carlo phase problem, due to the electron-electron Coulomb interaction, is controlled via the phaseless approximation, with a trial wave function

Local Basis Set Supercell Studies of (K,Na)NbO

\ensuremath{\mid}{\ensuremath{\Psi}}_{T}⟩

_3

. As in previous calculations, a mean-field single Slater determinant is used as

Solid Solutions

\ensuremath{\mid}{\ensuremath{\Psi}}_{T}⟩

Electronic structure and lattice distortion in PbMg1/3Nb2/3O3

. The method is formulated in the Hilbert space defined by any chosen one-particle basis. The present calculations use a plane wave basis under periodic boundary conditions with norm-conserving pseudopotentials. Computational details of the plane wave AF QMC method are presented. The isolated systems chosen here allow a systematic study of the various algorithmic issues. We show the accuracy of the plane wave method and discuss its convergence with respect to parameters such as the supercell size and plane wave cutoff. The use of standard norm-conserving pseudopotentials in the many-body AF QMC framework is examined.

Study of Atoms and Molecules with Auxiliary-Field Quantum Monte Carlo

Abstract To treat interacting quantum systems, it is often crucial to have accurate calculations beyond the mean-field level. Many-body simulations based on field-theoretical approaches are a promising tool for this purpose and are applied in several sub-fields of physics, in closely related forms. An major difficulty is the sign or phase problem, which causes the Monte Carlo variance to increase exponentially with system size. We address this issue in the context of auxiliary-field simulations of realistic electronic systems in condensed matter physics. We show how to use importance sampling of the complex fields to control the phase problem. An approximate approach is formulated with a trial determinant to constrain the paths in field space and completely eliminate the growth of the noise. For ab initio electronic structure calculations, this gives a many-body approach in the form of a “coherent” superposition of mean-field calculations, allowing direct incorporation of state-of-the-art technology from the latter (non-local pseudopotentials; high quality basis sets, etc.). In our test calculations, single Slater determinants from density functional theory or Hartree–Fock calculations were used as trial wave functions, with no additional optimization. The calculated dissociation energies of various molecules and the cohesive energy of bulk Si are in excellent agreement with experiment and are comparable to or better than the best existing theoretical results.