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

Ab-Initio Calculation of the Metal-Insulator Transition in Sodium rings and chains and in mixed Sodium-Lithium systems

We study how the Mott metal-insulator transition (MIT) is influenced when we deal with electrons with different angular momenta. For lithium we found an essential effect when we include $p$-orbitals in the description of the Hilbert space. We apply quantum-chemical methods to sodium rings and chains in order to investigate the analogue of a MIT, and how it is influenced by periodic and open boundaries. By changing the interatomic distance we analyse the character of the many-body wavefunction and the charge gap. In the second part we mimic a behaviour found in the ionic Hubbard model, where a transition from a band to a Mott insulator occurs. For that purpose we perform calculations for mixed sodium-lithium rings. In addition, we examine the question of bond alternation for the pure sodium system and the mixed sodium-lithium system, in order to determine under which conditions a Peierls distortion occurs.Comment: 8 pages, 7 figures, accepted Eur. J. Phys.

Calculation of the static and dynamical correlation energy of pseudo-one-dimensional beryllium systems via a many-body expansion

Low-dimensional beryllium systems constitute interesting case studies for the test of correlation methods because of the importance of both static and dynamical correlation in the formation of the bond. Aiming to describe the whole dissociation curve of extended Be systems we chose to apply the method of increments (MoI) in its multireference (MR) formalism. However, in order to do so an insight into the wave function was necessary. Therefore we started by focusing on the description of small Be chains via standard quantum chemical methods and gave a brief analysis of the main characteristics of their wave functions. We then applied the MoI to larger beryllium systems, starting from the Be6 ring. First, the complete active space formalism (CAS-MoI) was employed and the results were used as reference for local MR calculations of the whole dissociation curve. Despite this approach is well established for the calculation of systems with limited multireference character, its application to the description of whole dissociation curves still requires further testing. After discussing the role of the basis set, the method was finally applied to larger rings and extrapolated to an infinite chain

Correlated ab-initio calculations for ground-state properties of II-VI semiconductors

Correlated ab-initio ground-state calculations, using relativistic energy-consistent pseudopotentials, are performed for six II-VI semiconductors. Valence ($ns,np$) correlations are evaluated using the coupled cluster approach with single and double excitations. An incremental scheme is applied based on correlation contributions of localized bond orbitals and of pairs and triples of such bonds. In view of the high polarity of the bonds in II-VI compounds, we examine both, ionic and covalent embedding schemes for the calculation of individual bond increments. Also, a partitioning of the correlation energy according to local ionic increments is tested. Core-valence ($nsp,(n-1)d$) correlation effects are taken into account via a core-polarization potential. Combining the results at the correlated level with corresponding Hartree-Fock data we recover about 94% of the experimental cohesive energies; lattice constants are accurate to \sim 1%; bulk moduli are on average 10% too large compared with experiment.Comment: 10 pages, twocolumn, RevTex, 3 figures, accepted Phys. Rev.

Factors Associated with Hospital Readmissions Among United States Dialysis Facilities

Hospital readmissions are a major burden for patients with end stage renal disease (ESRD). On average, one in three hospital discharges among patients with ESRD are followed by a readmission within 30 days. Currently, dialysis facilities are held accountable for readmissions via the ESRD Quality Incentive Program standardized readmission ratio (SRR) clinical measure. However, little is known about facility-level factors associated with readmission. Additionally, unlike other standardized measures of quality in the dialysis setting, incident patients within their first 90-days of dialysis are included in the performance calculation. This study analyzed CMS Dialysis Facility Report data from 2013 to 2016 to examine dialysis facility and incident patient factors associated with SRR using multivariate mixed models. Among 5,419 dialysis facilities treating 104,768 incident patients, the mean SRR remained stable across all four study years at 0.99. Factors significantly associated with a lower SRR (p\u3c0.0001) included Western geographic region and higher patient care technician ratios. Several incident patient pre-dialysis nephrology care characteristics were associated with lower SRRs including higher percentages of patients with a fistula present at first dialysis treatment, higher percentages of patients receiving 6-12 months or greater than 12 months of nephrology care prior to dialysis and higher facility average hemoglobin. Factors significantly associated with a higher SRR (p\u3c0.0001) included Northeastern geographic region, higher registered nurse ratios, higher percentage of incident patients, and higher facility average GFR. Understanding facility-level and patient-level factors associated with higher SRRs may inform interventions to reduce 30-day hospital readmission among patients receiving dialysis

Struktur Kepemilikan, Mekanisme Tata Kelola Perusahaan, Dan Biaya Keagenan Di Indonesia (Studi Empirik Pada Perusahaan Di Bursa Efek Indonesia)

This study is to examine the effect of corporate governance (the owners\u27s character and thegovernance mechanism) on agency cost. This research shows that family ownership, financialinstitution ownership, government ownership, and foreign ownership have negative effects onagency cost that is proxied as managerial operation cost and or as assets turnover, compared topublic ownership. Furthermore, ownership concentration of at least 5 percent each is not provento effect the agency cost. Results of other examination show that the proportion of independentboard and the number of board meetings have negative effects to the agency cost that is proxiedas assets turnover. However, these two variables and the number of audit committee meetinghave the opposite effect to the agency cost when it is proxied as managerial operation cost.Theseinconsistencies are caused by the ineffective implementation of corporate governance mechanismin Indonesia even after 10 years of implementation