The study of the strength of correlations in NaxCoO2 is extended to the x = 0 end of the phase diagram where Mott insulating behavior has been widely anticipated. Inclusion of correlation as modeled by the LDA+U approach leads to a Mott transition in the ag subband if U≥Uc=2.5 eV. Thus U smaller than Uc is required to model the metallic, nonmagnetic CoO2 compound reported by Tarascon and cowork...

Principal Component Analysis (PCA) plus Linear Discriminant Analysis (LDA) (PCA+LDA) and LDA/QR are both two-stage methods that deal with the small sample size (SSS) problem in traditional LDA. When applied to face recognition under varying lighting conditions and different facial expressions, neither method may work robustly due to limited number of training samples for each class in the train...

The families of high-temperature superconductors recently welcomed a new member: hole-doped nickelate ${\mathrm{Nd}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{NiO}}_{2}$ with $\ensuremath{\sim}15\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ transition temperature. To understand its emergent low-energy behaviors and experimental properties, an immediate key question is whether the superconducting hole carriers...

Abstract The density-functional theory is widely used to predict the physical properties of materials. However, it usually fails for strongly correlated A popular solution use Hubbard correction treat electronic states. Unfortunately, values U and J parameters are initially unknown, they can vary from one material another. In this semi-empirical study, we explore parameter space a group iron-ba...

Recently, α-RuCl3 has attracted much attention as a possible material to realize the honeycomb Kitaev model of a quantum-spin-liquid state. Although the magnetic properties of α-RuCl3 have been extensively studied, its electronic structure, which is strongly related to its Kitaev physics, is poorly understood. Here, the electronic structure of α-RuCl3 was investigated by photoemission (PE) and ...

Optical properties of the isoelectronic compounds LaCoO3 and HoCoO3 has been experimentally and theoretically investigated. We’ve measured the real ε1(ω) and imaginary ε2(ω) parts of the dielectric function, reflectance R(ω) and optical conductivity at room temperature. The shift of the most pronounced spectral features to the high energy region on 0.3 eV associated with larger distortions due ...

In this paper, we present counterarguments against the direct LDA algorithm (D-LDA), which was previously claimed to be equivalent to Linear Discriminant Analysis (LDA). We show from Bayesian decision theory that D-LDA is actually a special case of LDA by directly taking the linear space of class means as the LDA solution. The pooled covariance estimate is completely ignored. Furthermore, we de...

With a series of local-density approximation plus Hubbard U calculations, we have demonstrated that for lanthanum cobaltite LaCoO3 , the electric field gradient at the cobalt nucleus can be used as a fingerprint to identify the spin state of the cobalt ion. Therefore, in principle, the spin state of the cobalt ion can be unambiguously determined from nuclear magnetic resonance spectra. Our calc...

We present a new approach to the evaluation of the on-site repulsion energy U for use in the LDA+U method of Anisimov and collaborators. Our objectives are to make the method more firmly based, to concentrate primarily on ground state properties rather than spectra, and to test the method in cases where only modest changes in orbital occupations are expected, as well as for highly correlated ma...