Biomedical subjects

Michele Casula

Publications and source records attributed to Michele Casula.

3 recordsLinked to original sources

PubMed2005

Charge and spin correlations of a one-dimensional electron gas on the continuum.

We present a variational Monte Carlo study of a model one-dimensional electron gas on the continuum, with long-range interaction (1/r decay). At low density, the reduced dimensionality brings about pseudonodes of the many-body wavefunction, yielding nonergodic behavior of naive Monte Carlo sampling, which affects the evaluation of pair correlations and the related structure factors. The problem is, however, easily solved, and we carefully analyzed the structure factors obtained from an optimal trial function, finding good agreement with the exact predictions for a Luttinger-like Hamiltonian with an interaction similar to the one used in the present study.

Journal Article↗

PubMed2005

Diffusion Monte Carlo method with lattice regularization.

We introduce an efficient lattice regularization scheme for quantum Monte Carlo calculations of realistic electronic systems. The kinetic term is discretized by a finite difference Laplacian with two mesh sizes, a and a', chosen so that the electrons can diffuse in a configuration space which is in practice indistinguishable from the continuum, and the different length scales in the system can be efficiently taken in account. The regularized Hamiltonian goes to the continuous limit for a --> 0 and allows the inclusion of nonlocal potentials in a consistent variational scheme, substantially improving the accuracy upon previous nonvariational approaches.

Journal Article↗

PubMed2004

Correlated geminal wave function for molecules: an efficient resonating valence bond approach.

We show that a simple correlated wave function, obtained by applying a Jastrow correlation term to an antisymmetrized geminal power, based upon singlet pairs between electrons, is particularly suited for describing the electronic structure of molecules, yielding a large amount of the correlation energy. The remarkable feature of this approach is that, in principle, several resonating valence bonds can be dealt simultaneously with a single determinant, at a computational cost growing with the number of electrons similar to more conventional methods, such as Hartree-Fock or density functional theory. Moreover we describe an extension of the stochastic reconfiguration method, which was recently introduced for the energy minimization of simple atomic wave functions. Within this extension the atomic positions can be considered as further variational parameters, which can be optimized together with the remaining ones. The method is applied to several molecules from Li(2) to benzene by obtaining total energies, bond lengths and binding energies comparable with much more demanding multiconfiguration schemes.

Journal Article↗