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We investigate strong electron-electron correlation effects on 2-dimensional van der Waals materials Nb$_3$X$_8$ (X=Cl, Br, I). We find that the monolayers Nb$_3$X$_8$ are ideal systems close to the strong correlation limit. They can be…
Computational studies have shown that one or more positrons can stabilize two repelling atomic anions through the formation of two-center positronic bonds. In the present work, we study the energetic stability of a system containing two…
First-principles calculations for carbyne under strain predict that the Peierls transition from symmetric cumulene to broken-symmetry polyyne structure is enhanced as the material is stretched. Interpretation within a simple and instructive…
We demonstrate the importance of electron correlation effects in the hyperfine structure constants of many low-lying states in $^{210}$Fr and $^{212}$Fr. This is achieved by calculating the magnetic dipole and electric quadrupole hyperfine…
By using the determinant Quantum Monte Carlo method, the magnetic and pairing correlation of the Na$_{x}$CoO$_{2}\cdot$yH$_{2}$O system are studied within the Hubbard model on a bilayer triangular lattice. The temperature dependence of spin…
Tensile stress relaxation is combined with transmission electron microscopy to reveal dramatic changes in dislocation structure and sub structure in pure alpha iron as a result of the effects of dissolved hydrogen. We find that hydrogen…
A rectangular plate of dielectric elastomer exhibiting gradients of material properties through its thickness will deform inhomogeneously when a potential difference is applied to compliant electrodes on its major surfaces, because each…
Quantum Monte Carlo methods are used to study a quantum phase transition in a 1D Hubbard model with a staggered ionic potential (D). Using recently formulated methods, the electronic polarization and localization are determined directly…
Using the Constrained Path Monte Carlo (CPMC) method, we simulated the two-dimensional, three-band Hubbard model to study pairing, charge, and spin correlations as a function of electron and hole doping and the Coulomb repulsion $V_{pd}$…
We consider the Hubbard-Holstein model in the adiabatic limit to investigate the effects of electron-electron interactions on the electron-phonon coupling. To this aim we compute at any momentum and filling the static charge susceptibility…
We propose a simple and accurate model for the electron static structure factors (and corresponding pair-correlation functions) of the 3D unpolarized homogeneous electron gas. Our spin-resolved pair-correlation function is built up with a…
The effects of the spin and lattice degrees of freedom on the electronic structure of M1 vanadium dioxide are explored using a quasiparticle description. Contraction of the inter-vanadium spacing of the Peierls pairings stabilizes bonding…
We study correlations on the euclidean spacetimes generated in Monte Carlo simulations of the model. In the elongated phase, curvature correlations appear to fall off like a fractional power. Near the transition to the crumpled phase this…
The electronic structure of C_(4N+2) carbon rings exhibits competing many-body effects of Huckel aromaticity, second-order Jahn-Teller and Peierls instability at large sizes. This leads to possible ground state structures with aromatic,…
The onset of distortion in one-dimensional monatomic chains with partially filled valence bands is considered to be well-established by the Peierls theorem, which associates the distortion with the formation of a band gap and a subsequent…
A possibility of the electronic origin of the high-temperature superconductivity in cuprates is probed with the quantum Monte Carlo method by revisiting the three-band Hubbard model comprising Cu$3d_{x^2-y^2}$ and O$2p_\sigma$ orbitals. The…
We investigate the ground-state properties of the two-dimensional Hubbard model, based on the off-diagonal wave function variational Monte Carlo method. We use an optimized wave function that is improved from an initial one-body wave…
Peierls-type instabilities in quarter-filled ($\bar{n}=1/2$) and half-filled ($\bar{n}=1$) quantum double-well hydrogen-bonded chain are investigated analytically in the framework of two-stage orientational-tunnelling model with additional…
Perturbative corrections to the mean field theory for particle-hole instabilities of interacting electron systems are computed within a scheme which is equivalent to the recently developed variational approach to the Kohn-Luttinger…
We analyze several properties of the lattice solitons in the incommensurate phase of spin-Peierls systems using exact diagonalization and quantum Monte Carlo. These systems are modelled by an antiferromagnetic Heisenberg chain with nearest…