arXiv subjects

E. L. Pollock

Publications and source records attributed to E. L. Pollock.

6 recordsLinked to original sources

arXiv2003

Path Integral Monte Carlo Calculation of the Momentum Distribution of the Homogeneous Electron Gas at Finite Temperature

Path integral Monte Carlo (PIMC) simulations are used to calculate the momentum distribution of the homogeneous electron gas at finite temperature. This is done by calculating the off-diagonal elements of the real-space density matrix, represented in PIMC by open paths. It is demonstrated how the restricted path integral Monte Carlo methods can be extended in order to deal with open paths in fermionic systems where a sign problem is present. The computed momentum distribution shows significant deviations for strong correlation from free fermion results but agrees with predictions from variational methods.

cond-mat.stat-mech↗

arXiv2002

Lowering of the Kinetic Energy in Interacting Quantum Systems

Interactions never lower the ground state kinetic energy of a quantum system. However, at nonzero temperature, where the system occupies a thermal distribution of states, interactions can reduce the kinetic energy below the noninteracting value. This can be demonstrated from a first order weak coupling expansion. Simulations (both variational and restricted path integral Monte Carlo) of the electron gas model and dense hydrogen confirm this and show that in contrast to the ground state case, at nonzero temperature the population of low momentum states can be increased relative to the free Fermi distribution. This effect is not seen in simulations of liquid He-3.

cond-mat.stat-mech↗

arXiv1999

Variational Density Matrix Method for Warm Condensed Matter and Application to Dense Hydrogen

A new variational principle for optimizing thermal density matrices is introduced. As a first application, the variational many body density matrix is written as a determinant of one body density matrices, which are approximated by Gaussians with the mean, width and amplitude as variational parameters. The method is illustrated for the particle in an external field problem, the hydrogen molecule and dense hydrogen where the molecular, the dissociated and the plasma regime are described. Structural and thermodynamic properties (energy, equation of state and shock Hugoniot) are presented.

physics.plasm-ph↗

arXiv1998

Volume-Collapse Transitions in the Rare Earth Metals

We describe current experimental and theoretical understanding of the pressure-induced volume collapse transitions occurring in the early trivalent rare earth metals. General features of orbitally realistic mean-field based theories used to calculate these transitions are discussed. Potential deficiencies of these methods are assessed by comparing mean field and exact Quantum Monte Carlo solutions for the one-band Hubbard and two-band periodic Anderson lattice models. Relevant parameter regimes for these models are determined from local density constrained occupation calculations.

cond-mat.str-el↗

arXiv1995

Comments on PPPM, FMM, and the Ewald Method for Large Periodic Coulombic Systems

The three most common methods, Ewald, fast multipole (FMM) and the particle-particle particle-mesh (PPPM), used to compute the interactions in many body Coulombic systems are compared for single and multi-processor machines. The Ewald method is recommended for systems of a few hundred particles per processor or less. For larger systems the PPPM method is suggested. The FMM is slower and more difficult to code efficiently.

cond-mat↗

arXiv1995

Inhomogeneity and Current Corrections to a Non-uniform Electronic System in Strong Magnetic Fields

Using the polarizability of a free electron gas in a magnetic field and the Current-Density Functional Theory (CDFT) developed by Vignale and Rasolt, we derive the gradient and current corrections for the energy functional of a non-uniform electronic system in a strong magnetic field. First, we find the Tomishima-Shinjo functional by neglecting the current variation. Taking into account the current variation leads to new gradient terms which change contraction effects in the direction perpendicular to the magnetic field.

cond-mat↗