arXiv subjects

Zhishuo Huang

Publications and source records attributed to Zhishuo Huang.

11 recordsLinked to original sources

arXiv2025

Breakdown of broken-symmetry approach to exchange interaction

Broken-symmetry (BS) approaches are widely employed to evaluate Heisenberg exchange parameters, primarily in combination with DFT calculations. For many magnetic materials, BS-DFT calculations give reasonable estimations of exchange parameters, although systematic failures have also been reported. While the latter were attributed to deficiencies of approximate exchange-correlation functional, we prove here by treating a simple model system that the broken-symmetry methodology has serious problems. Detailed analysis clarifies the intrinsic issue with the broken-symmetry treatment of low-spin states. It shows, in particular, that the error in the BS calculation of exchange parameter scales with the degree of covalency between the magnetic and the bridging orbitals. This is due to the constraint on the form of multiconfigurational state imposed by the BS determinant, a feature common to other single-reference methods too. As a possible tool to overcome this intrinsic drawback of single-determinant BS approaches, we propose their extension to a minimal multiconfigurational version.

physics.chem-ph↗

arXiv2024

New tool for extraction of $^{187}$Os Mössbauer parameters with biologically relevant detection sensitivity

A large number of osmium complexes with osmium in different oxidation states (II, III, IV, VI) have been reported recently to exhibit good antiproliferative activity in cancer cell lines. Herein, we demonstrate new opportunities offered by $^{187}$Os nuclear forward scattering (NFS) and nuclear inelastic scattering (NIS) of synchrotron radiation for characterization of hyperfine interactions and lattice dynamics in a benchmark Os(VI) complex K$_2$[OsO$_2$(OH)$_4$], by accurate extraction of Mössbauer parameters and the determination of Os-projected density of phonon states confirmed by first-principles phonon calculations. The values of isomer shift ($δ$ = 3.3(1) mm/s) relative to [Os$^{IV}$ Cl$_{6}$]$^{2-}$ and quadrupole splitting ($ΔE_Q$ = 12.0(2) mm/s) were determined with NFS, while the Lamb-Mössbauer factor (0.55(1)), the density of phonon states (DOS), and a full thermodynamics characterization was carried out using the NIS data combined with first principle theoretical calculations. In more general terms, this study provides strong evidence that $^{187}$Os nuclear resonance scattering is a reliable technique for the investigation of hyperfine interactions and Os specific vibrations in osmium(VI) species, which might be potentially applicable for measuring such interactions in osmium complexes of other oxidation states, including those with anticancer activity such as Os(III) and Os(IV).

cond-mat.mtrl-sci↗

arXiv2024

First-principles derivation of elastic interaction between Jahn-Teller centers in crystals via lattice Green's functions

Jahn-Teller (JT) systems with strong and intermediate vibronic coupling are described in terms of local JT active vibrational modes. In JT crystals, the elastic interaction of these modes at different JT centers plays a crucial role, for instance, in determining critical temperature of structural phase transitions. Despite their importance, the parameters of elastic interaction between JT centers have not been accessed yet by first-principles calculations. In this paper, we develop an effective Hamiltonian methodology for the thorough description of the elastic interactions in cooperative Jahn-Teller problems, which treats the interactions with both phonons and uniform strains. All the microscopic parameters, such as lattice Green's functions, elastic modulus, can be obtained or calculated based on first-principles the calculation. The method has been applied to a series of 5d1 double perovskites. Such effective Hamiltonian methodology can be, in general, used to investigate the APES of any type of the local distortions, such as impurities, defects, etc.

cond-mat.mtrl-sci↗

arXiv2022

Multipolar exchange interaction and complex order in insulating lanthanides

In insulating lanthanides, unquenched orbital momentum and weak crystal-field (CF) splitting of the atomic $J$ multiplet at lanthanide ions result in a highly ranked (multipolar) exchange interaction between them and a complex low-temperature magnetic order not fully uncovered by experiment. Explicitly correlated {\it ab initio } methods proved to be highly efficient for an accurate description of CF multiplets and magnetism of individual lanthanide ions in such materials. Here we extend this {\it ab initio } methodology and develop a first-principles microscopic theory of multipolar exchange interaction between $J$-multiplets in $f$ metal compounds. The key point of the approach is a complete account of Goodenough's exchange mechanism along with traditional Anderson's superexchange and other contributions, the former being dominant in many lanthanide materials. Application of this methodology to the description of the ground-state order in the neodymium nitride with rocksalt structure reveals the multipolar nature of its ferromagnetic order. We found that the primary and secondary order parameters (of $T_{1u}$ and $E_g$ symmetry, respectively) contain non-negligible $J$-tensorial contributions up to the ninth order. The calculated spin-wave dispersion and magnetic and thermodynamic properties show that they cannot be simulated quantitatively by confining to the ground CF multiplet on the Nd sites. Our results demonstrate that the {\it ab initio } approach to the low-energy Hamiltonian represents a powerful tool for the study of materials with complex magnetic order.

cond-mat.str-el↗

arXiv2021

Jahn-Teller effect in cubic fullerides A$_{3}$C$_{60}$

Compared to isolated C$_{60}^{3-}$ ions, characterized by a threedimensional equipotential trough at the bottom of the lowest adiabatic potential energy surface (APES), the Jahn-Teller (JT) effect in cubic fullerides is additionally influenced by the interaction of JT distortions at C$_{60}$ sites with vibrational modes of the lattice. This leads to modification of JT stabilization energy and to the warping of the trough at each fullerene site, as well as to the interaction of JT distortions at different sites. Here we investigate these effects in three fcc fullerides with A=K,Rb,Cs and in Cs$_3$C$_{60}$ with bcc (A15) structure. DFT calculations of orbital vibronic coupling constants at C$_{60}$ sites and of phonon spectra have been done for fully ordered lattices (1 C$_{60}$/u.c.). Based on them the elastic response function for local JT distortions has been evaluated and the lowest APES investigated. To this end an expression for the latter in function of trough coordinates of all sites has been derived. The results show that the JT stabilization energy slightly increases compared to an isolated C$_{60}^{3-}$ and a warping of the trough of few meV occurs. The interaction of JT distortions on nearest- and next-nearest-neighbor fullerene sites is of similar order of magnitude. These effects arise first of all due to the interaction of C$_{60}$ sites with the displacements of neighbor alkali atoms and are more pronounced in fcc fullerides than in the A15 compound. The results of this study support the picture of weakly hindered independent rotations of JT deformations at C$_{60}$ sites in cubic A$_3$C$_{60}$.

cond-mat.str-el↗

arXiv2020

Ferromagnetic kinetic exchange interaction in magnetic insulators

The superexchange theory predicts dominant antiferromagnetic kinetic interaction when the orbitals accommodating magnetic electrons are covalently bonded through diamagnetic bridging atoms/groups. Here we show that explicit consideration of magnetic and (leading) bridging orbitals, together with the electron transfer between the former, reveals a strong ferromagnetic kinetic exchange contribution. First principle calculations show that it is comparable in strength with antiferromagnetic superexchange in a number of magnetic materials with diamagnetic metal bridges. In particular, it is responsible for a very large ferromagnetic coupling ($-10$ meV) between the iron ions in a Fe$^{3+}$-Co$^{3+}$-Fe$^{3+}$ complex.

cond-mat.str-el↗

arXiv2020

First principles study of the vibronic coupling in positively charged C$_{60}^+$

Vibronic coupling parameters for C$_{60}^{+}$ were derived via DFT calculations with hybrid B3LYP and CAM-B3LYP functional, based on which the static Jahn-Teller effect were analyzed. The global minima of adiabatic potential energy surface (APES) shows a D$_{5d}$ Jahn-Teller deformation, with stabilization energies of 110 and 129 meV (with B3LYP and CAM-B3LYP respectively), which are two times larger than that in C$_{60}^-$, suggesting the crucial role of the dynamical Jahn-Teller effect. Present results enable us to assess the actual situation of dynamical Jahn-Teller effect in C$_{60}^{+}$ and excited C$_{60}$ in combination with the established parameters for C$_{60}^{-}$.

physics.chem-ph↗

arXiv2019

Dynamical Jahn-Teller effect in the first excited C$_{60}^-$

The Jahn-Teller effect of C$_{60}$ anions in the first electronically excited states was theoretically investigated. The orbital vibronic coupling parameters for the $t_{1g}$ next lowest unoccupied molecular orbitals were derived from the Kohn-Sham orbital levels with hybrid B3LYP functional by using the frozen phonon approach. With the use of these coupling parameters, the vibronic states of the first excited C$_{60}^-$ were derived by exactly diagonalizing the dynamical Jahn-Teller Hamiltonian. The dynamical Jahn-Teller stabilization energy of the first excited C$_{60}^-$ is stronger than that of the ground electronic states.

physics.chem-ph↗

arXiv2016

Band gap engineering of PtSe2

Besides its predicted promising high electron mobilities at room temperature, PtSe2 bandgap sensitively depends on the number of monolayers combined by van der Waals interaction according to our calculations. We understand this by using bandstructure calculations based on the density functional theory. It was found that the front orbitals of VBM and CBM are contributed mainly from pz and px+y orbitals of Se which are sensitive to the out-plane and in-plane lattice constants, respectively. The van der Waals force enhances the bonding out-of-plane, which in-turn influences the bonding in-plane. We found that the thickness dependent bandgap has the same origin as the strain dependent bandgap, which is from the change of the front orbital interactions. The work shows the flexibilities of tuning the electronic and optical properties of this compound in a wide range.

cond-mat.mtrl-sci↗

arXiv2015

Screening for Two dimensional MX$_2$ semiconductors with possible high room temperature mobility

We calculated the electron mobility of 14 two dimensional semiconductors with composition of MX$_2$, where M (= Mo, W, Sn, Hf, Zr and Pt) is the transition metal, and X is S, Se and Te. We treated the scattering matrix by deformation potential approximation. Long wave longitudinal acoustical and optical phonon scatterings are included. Piezoelectric scattering in the compounds without inversion symmetry is also taken into account. We found that out of the 14 compounds, WSe$_2$, PtS$_2$ and PtSe$_2$, are promising regarding to the possible high electron mobility and finite band gap. The phonon limited mobility in PtSe$_2$ reaches about 3000 cm$^2$V$^{-1}$s$^{-1}$ at room temperature which is the highest among the compounds. The bandgap under the local density approximation is 1.25 eV. Our results can be a guide for experiments to search for better two-dimensional materials for future semiconductor devices.

cond-mat.mtrl-sci↗

arXiv2014

Two dimensional semiconductors with possible high room temperature mobility

We calculated the longitudinal acoustic phonon limited electron mobility of 14 two dimensional semiconductors with composition of MX$_2$, where M (= Mo, W, Sn, Hf, Zr and Pt) is the transition metal, and X is S, Se and Te. We treated the scattering matrix by deformation potential approximation. We found that out of the 14 compounds, MoTe$_2$, HfSe$_2$ and HfTe$_2$, are promising regarding to the possible high mobility and finite band gap. The phonon limited mobility can be above 2500 cm$^2$V$^{-1}$s$^{-1}$ at room temperature.

cond-mat.mtrl-sci↗