107 research outputs found
Investigation of metal-insulator like transition through the ab initio density matrix renormalization group approach
We have studied the Metal-Insulator like Transition (MIT) in lithium and
beryllium ring-shaped clusters through ab initio Density Matrix Renormalization
Group (DMRG) method. Performing accurate calculations for different interatomic
distances and using Quantum Information Theory (QIT) we investigated the
changes occurring in the wavefunction between a metallic-like state and an
insulating state built from free atoms. We also discuss entanglement and
relevant excitations among the molecular orbitals in the Li and Be rings and
show that the transition bond length can be detected using orbital entropy
functions. Also, the effect of different orbital basis on the effectiveness of
the DMRG procedure is analyzed comparing the convergence behavior.Comment: 12 pages, 14 figure
Phase Separation of Superfluids in the Chain of Four-Component Ultracold Atoms
We investigate the competition of various exotic superfluid states in a chain
of spin-polarized ultracold fermionic atoms with hyperfine spin and
s-wave contact interactions. We show that the ground state is an exotic
inhomogeneous mixture in which two distinct superfluid phases --- spin-carrying
pairs and singlet quartets --- form alternating domains in an extended region
of the parameter space
Emergence of Quintet Superfluidity in the Chain of Partially Polarized Spin-3/2 Ultracold Atom
The system of ultracold atoms with hyperfine spin might be unstable
against the formation of quintet pairs if the interaction is attractive in the
quintet channel. We have investigated the behavior of correlation functions in
a model including only s-wave interactions at quarter filling by large-scale
density-matrix renormalization-group simulations. We show that the correlations
of quintet pairs become quasi-long-ranged, when the system is partially
polarized, leading to the emergence of various mixed superfluid phases in which
BCS-like pairs carrying different magnetic moment coexist.Comment: 4 pages, 4 figures; significantly rewritten compared to the first
versio
On the dimerized phase in the cross-coupled antiferromagnetic spin ladder
We revisit the phase diagram of the frustrated s=1/2 spin ladder with
antiferromagnetic rung and diagonal couplings. In particular, we reexamine the
evidence for the columnar dimer phase, which has been predicted from analytic
treatment of the model and has been claimed to be found in numerical
calculations. By considering longer chains and by keeping more states than in
previous work using the density-matrix renormalization group, we show that the
numerical evidence presented previously for the existence of the dimerized
phase is not unambiguous in view of the present more careful analysis. While we
cannot completely rule out the possibility of a dimerized phase in the
cross-coupled ladder, we do set limits on the maximum possible value of the
dimer order parameter that are much smaller than those found previously.Comment: 6 pages, 7 figure
On the calculation of complete dissociation curves of closed-shell pseudo- onedimensional systems via the complete active space method of increments
The method of increments (MoI) has been employed using the complete active
space formalism in order to calculate the dissociation curve of beryllium
ring-shaped clusters Be n of different sizes. Benchmarks obtained through
different quantum chemical methods including the ab initio density matrix
renormalization group were used to verify the validity of the MoI truncation
which showed a reliable behavior for the whole dissociation curve. Moreover we
investigated the size dependence of the correlation energy at different
interatomic distances in order to extrapolate the values for the periodic
chain and to discuss the transition from a metal-like to an insulator-like
behavior of the wave function through quantum chemical considerations
Magneto-elastic coupling and competing entropy changes in substituted CoMnSi metamagnets
We use neutron diffraction, magnetometry and low temperature heat capacity to
probe giant magneto-elastic coupling in CoMnSi-based antiferromagnets and to
establish the origin of the entropy change that occurs at the metamagnetic
transition in such compounds. We find a large difference between the electronic
density of states of the antiferromagnetic and high magnetisation states. The
magnetic field-induced entropy change is composed of this contribution and a
significant counteracting lattice component, deduced from the presence of
negative magnetostriction. In calculating the electronic entropy change, we
note the importance of using an accurate model of the electronic density of
states, which here varies rapidly close to the Fermi energy.Comment: 11 pages, 9 figures. Figures 4 and 6 were updated in v2 of this
preprint. In v3, figures 1 and 2 have been updated, while Table II and the
abstract have been extended. In v4, Table I has updated with relevant neutron
diffraction dat
Comparison of approximate intermolecular potentials for ab initio fragment calculations on medium sized N‐heterocycles
The ground state intermolecular potential of bimolecular complexes of N‐heterocycles is analyzed for the impact of individual terms in the interaction energy as provided by various, conceptually different theories. Novel combinations with several formulations of the electrostatic, Pauli repulsion, and dispersion contributions are tested at both short‐ and long‐distance sides of the potential energy surface, for various alignments of the pyrrole dimer as well as the cytosine–uracil complex. The integration of a DFT/CCSD density embedding scheme, with dispersion terms from the effective fragment potential (EFP) method is found to provide good agreement with a reference CCSD(T) potential overall; simultaneously, a quantum mechanics/molecular mechanics approach using CHELPG atomic point charges for the electrostatic interaction, augmented by EFP dispersion and Pauli repulsion, comes also close to the reference result. Both schemes have the advantage of not relying on predefined force fields; rather, the interaction parameters can be determined for the system under study, thus being excellent candidates for ab initio modeling
Quantum information analysis of electronic states at different molecular structures
We have studied transition metal clusters from a quantum information theory
perspective using the density-matrix renormalization group (DMRG) method. We
demonstrate the competition between entanglement and interaction localization.
We also discuss the application of the configuration interaction based
dynamically extended active space procedure which significantly reduces the
effective system size and accelerates the speed of convergence for complicated
molecular electronic structures to a great extent. Our results indicate the
importance of taking entanglement among molecular orbitals into account in
order to devise an optimal orbital ordering and carry out efficient
calculations on transition metal clusters. We propose a recipe to perform DMRG
calculations in a black-box fashion and we point out the connections of our
work to other tensor network state approaches
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