59 research outputs found
Graphical dynamic trends for earthquake incidence response of plan-asymmetric systems
A Graphical Dynamic model is derived to describe the directional earthquake response of two-ways plan-asymmetric systems, which retains the insightful educational evidence of traditional graphical static methods and the accuracy of computational methods of analysis. The dynamic directional response is expressed in terms of modal rotational kinematics about modal centers of rotation, referred to as modal torsional pivots. Seismic forces and response decomposition are handled through geometric modal torsional trends and the earthquake incidence response envelopes are described through directional modal participation radii and graphic spectrum-based "8-shaped" directional influence circles. The graphic approach provides good predictions of the maximum response and of the critical angle computed through CQC3 and other directional analysis methods
Solidification of small para-H2 clusters at zero temperature
We have determined the ground-state energies of para-H clusters at zero
temperature using the diffusion Monte Carlo method. The liquid or solid
character of each cluster is investigated by restricting the phase through the
use of proper importance sampling. Our results show inhomogeneous
crystallization of clusters, with alternating behavior between liquid and solid
phases up to N=55. From there on, all clusters are solid. The ground-state
energies in the range N=13--75 are established and the stable phase of each
cluster is determined. In spite of the small differences observed between the
energy of liquid and solid clusters, the corresponding density profiles are
significantly different, feature that can help to solve ambiguities in the
determination of the specific phase of H clusters.Comment: 17 pages, accepted for publication in J. Phys. Chem.
Digital Quantum Simulation of the Holstein Model in Trapped Ions
We propose the implementation of the Holstein model by means of digital
methods in a linear chain of trapped ions. We show how the simulation fidelity
scales with the generation of phononic excitations. We propose a decomposition
and a stepwise trapped-ion implementation of the Holstein Hamiltonian. Via
numerical simulations, we study how the protocol is affected by realistic
gates. Finally, we show how measurements of the size of the simulated polaron
can be performed.Comment: 5 pages + supplemental material, 3+3 figures. Accepted in Physical
Review Letter
Ground-state properties of the spin-1/2 antiferromagnetic Heisenberg model on the triangular lattice: A variational study based on entangled-plaquette states
We study, on the basis of the general entangled-plaquette variational ansatz,
the ground-state properties of the spin-1/2 antiferromagnetic Heisenberg model
on the triangular lattice. Our numerical estimates are in good agreement with
available exact results and comparable, for large system sizes, to those
computed via the best alternative numerical approaches, or by means of
variational schemes based on specific (i.e., incorporating problem dependent
terms) trial wave functions. The extrapolation to the thermodynamic limit of
our results for lattices comprising up to N=324 spins yields an upper bound of
the ground-state energy per site (in units of the exchange coupling) of
[ for the XX model], while the estimated
infinite-lattice order parameter is (i.e., approximately 64% of the
classical value).Comment: 8 pages, 3 tables, 2 figure
On the possible "supersolid" character of parahydrogen clusters
We present results of a theoretical study of structural and superfluid
properties of parahydrogen clusters comprising 25, 26 and 27 molecules at low
temperature. The microscopic model utilized here is based on the
Silvera-Goldman pair potential. Numerical results are obtained by means of
Quantum Monte Carlo simulations, making use of the continuous-space Worm
Algorithm. The clusters are superfluid in the low temperature limit, but
display markedly different physical behaviours. For N=25 and 27, superfluidity
at low temperature arises as clusters melt, i.e., become progressively
liquid-like as a result of quantum effects. On the other hand, for N = 26 the
cluster remains rigid and solid-like. We argue that this cluster can be
regarded as a mesoscopic "supersolid". This physical picture is supported by
results of simulations in which a single parahydrogen molecule in the cluster
is isotopically substituted.Comment: 18 pages, 7 figure
Quantum Simulation of Interacting Fermion Lattice Models in Trapped Ions
We propose a method of simulating efficiently many-body interacting fermion
lattice models in trapped ions, including highly nonlinear interactions in
arbitrary spatial dimensions and for arbitrarily distant couplings. We map
products of fermionic operators onto nonlocal spin operators and decompose the
resulting dynamics in efficient steps with Trotter methods, yielding an overall
protocol that employs only polynomial resources. The proposed scheme can be
relevant in a variety of fields as condensed-matter or high-energy physics,
where quantum simulations may solve problems intractable for classical
computers.Comment: 5 pages, 2 figures + Supplementary Materia
Thin helium film on a glass substrate
We investigate by Monte Carlo simulations the structure, energetics and
superfluid properties of thin helium-four films (up to four layers) on a glass
substrate, at low temperature. The first adsorbed layer is found to be solid
and "inert", i.e., atoms are localized and do not participate to quantum
exchanges. Additional layers are liquid, with no clear layer separation above
the second one. It is found that a single helium-three impurity resides on the
outmost layer, not significantly further away from the substrate than
helium-four atoms on the same layer.Comment: Six figures, submitted for publication to the Journal of Low
Temperature Physic
Complete-Graph Tensor Network States: A New Fermionic Wave Function Ansatz for Molecules
We present a new class of tensor network states that are specifically
designed to capture the electron correlation of a molecule of arbitrary
structure. In this ansatz, the electronic wave function is represented by a
Complete-Graph Tensor Network (CGTN) ansatz which implements an efficient
reduction of the number of variational parameters by breaking down the
complexity of the high-dimensional coefficient tensor of a
full-configuration-interaction (FCI) wave function. We demonstrate that CGTN
states approximate ground states of molecules accurately by comparison of the
CGTN and FCI expansion coefficients. The CGTN parametrization is not biased
towards any reference configuration in contrast to many standard quantum
chemical methods. This feature allows one to obtain accurate relative energies
between CGTN states which is central to molecular physics and chemistry. We
discuss the implications for quantum chemistry and focus on the spin-state
problem. Our CGTN approach is applied to the energy splitting of states of
different spin for methylene and the strongly correlated ozone molecule at a
transition state structure. The parameters of the tensor network ansatz are
variationally optimized by means of a parallel-tempering Monte Carlo algorithm
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