76,582 research outputs found
Simple vertex correction improves GW band energies of bulk and two-dimensional crystals
The GW self-energy method has long been recognized as the gold standard for
quasiparticle (QP) calculations of solids in spite of the fact that the neglect
of vertex corrections and the use of a DFT starting point lacks rigorous
justification. In this work we remedy this situation by including a simple
vertex correction that is consistent with an LDA starting point. We analyse the
effect of the self-energy by splitting it into a short-range and long-range
term which are shown to govern respectively the center and size of the band
gap. The vertex mainly improves the short-range correlations and therefore has
a small effect on the band gap, while it shifts the band gap center up in
energy by around 0.5 eV in good agreement with experiments. Our analysis also
explains how the relative importance of short- and long-range interactions in
structures of different dimensionality is reflected in their QP energies.
Inclusion of the vertex comes at practically no extra computational cost and
even improves the basis set convergence compared to GW. The method thus
provides an efficient and rigorous improvement over the GW approximation and
sets a new standard for quasiparticle calculations of solids
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
Contact interaction in an unitary ultracold Fermi gas
An ultracold Fermi atomic gas at unitarity presents universal properties that
in the diluted limit can be well described by a contact interaction. By
employing a guide function with correct boundary conditions and making simple
modifications to the sampling procedure we are able to handle for the first
time a true contact interaction in a quantum Monte Carlo calculation. The
results are obtained with small variances. Our calculations for the Bertsch and
contact parameters are in excellent agreement with published experiments. The
possibility of using a more faithfully description of ultracold atomic gases
can help uncover features yet unknown of the ultracold atomic gases. In
addition, this work paves the way to perform quantum Monte Carlo calculations
for systems interacting with contact interactions, where in many cases the
description using potentials with finite effective range might not be accurate
Nonequilibrium gas-liquid transition in the driven-dissipative photonic lattice
We study the nonequilibrium steady state of the driven-dissipative
Bose-Hubbard model with Kerr nonlinearity. Employing a mean-field decoupling
for the intercavity hopping , we find that the steep crossover between low
and high photon-density states inherited from the single cavity transforms into
a gasliquid bistability at large cavity-coupling . We formulate a van der
Waals like gasliquid phenomenology for this nonequilibrium situation and
determine the relevant phase diagrams, including a new type of diagram where a
lobe-shaped boundary separates smooth crossovers from sharp, hysteretic
transitions. Calculating quantum trajectories for a one-dimensional system, we
provide insights into the microscopic origin of the bistability.Comment: 5 pages, 4 figures + Supplemental Material (2 pages, 2 figures
- …