129 research outputs found
Diffusion Monte Carlo study of the equation of state of solid ortho-D
We present results of Diffusion Monte Carlo calculations for a system of
solid ortho-D_2 at different densities, for pressure ranging from 0 up to
350MPa. We compare the equation of state obtained using two of the most used
effective intermolecular potentials, i.e. the Silvera--Goldman and the Buck
potentials, with experimental data, in order to assess the validity of the
model interactions. The Silvera-Goldman potential has been found to provide a
satisfactory agreement with experimental results, showing that, as opposed to
what recently found for p-H_2, three--body forces can be efficiently accounted
for by an effective two--body term.Comment: 11 pages, 4 figure
Auxiliary Field Diffusion Monte Carlo calculation of nuclei with A<40 with tensor interactions
We calculate the ground-state energy of 4He, 8He, 16O, and 40Ca using the
auxiliary field diffusion Monte Carlo method in the fixed phase approximation
and the Argonne v6' interaction which includes a tensor force. Comparison of
our light nuclei results to those of Green's function Monte Carlo calculations
shows the accuracy of our method for both open and closed shell nuclei. We also
apply it to 16O and 40Ca to show that quantum Monte Carlo methods are now
applicable to larger nuclei.Comment: 4 pages, no figure
Ab-initio Dynamics of Rare Thermally Activated Reactions
We introduce a framework to investigate ab-initio the dynamics of rare
thermally activated reactions. The electronic degrees of freedom are described
at the quantum-mechanical level in the Born-Oppenheimer approximation, while
the nuclear degrees of freedom are coupled to a thermal bath, through a
Langevin equation. This method is based on the path integral representation for
the stochastic dynamics and yields the time evolution of both nuclear and
electronic degrees of freedom, along the most probable reaction pathways,
without spending computational time to explore metastable states. This approach
is very efficient and allows to study thermally activated reactions which
cannot be simulated using ab-initio molecular dynamics techniques. As a first
illustrative application, we characterize the dominant pathway in the
cyclobutene to butadiene reaction.Comment: 4 pages, 4 figure
Fermionic Shadow Wavefunction Variational calculations of the vacancy formation energy in He
We present a novel technique well suited to study the ground state of
inhomogeneous fermionic matter in a wide range of different systems. The system
is described using a Fermionic Shadow wavefunction (FSWF) and the energy is
computed by means of the Variational Monte Carlo technique. The general form of
FSWF is useful to describe many--body systems with the coexistence of different
phases as well in the presence of defects or impurities, but it requires
overcoming a significant sign problem. As an application, we studied the energy
to activate vacancies in solid He.Comment: 4 pages, 2 figure
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