Born Effective Charge Tensors Research Articles

Ab initio pressure-dependent vibrational and dielectric properties of chalcopyrite CuAlS2

We have performed an ab initio study of pressure-dependent lattice dynamical properties of chalcopyrite semiconductor $\mathrm{Cu}\mathrm{Al}{\mathrm{S}}_{2}$. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. Born effective charge tensors, dielectric permitivity tensors, the phonon frequencies at the Brillouin zone center, and their Gr\"uneisen parameters are calculated using density functional perturbation theory. We compare the Gr\"uneisen parameters of the calculated quantities with those of zinc-blende type materials and found similar trends.

First-principles study on lithium borohydrideLiBH4

First-principles calculations have been performed on lithium borohydride $\mathrm{Li}\mathrm{B}{\mathrm{H}}_{4}$ using the ultrasoft pseudopotential method, which is a potential candidate for hydrogen storage materials due to its extremely large gravimetric capacity of $18\phantom{\rule{0.3em}{0ex}}\text{mass}\phantom{\rule{0.3em}{0ex}}%$ hydrogen. We focus on an orthorhombic phase observed at ambient conditions and predict its fundamental properties; the structural properties, electronic properties, dielectric properties, vibrational properties, and the heat of formation. The calculation gives a nearly ideal tetrahedral shape for $\mathrm{B}{\mathrm{H}}_{4}$ complexes, although the recent experiment suggests that their configuration is strongly distorted [J-Ph. Souli\'e et al., J. Alloys Compd. 346, 200 (2002)]. Analyses for the electronic structure and the Born effective charge tensors indicate that Li atoms are ionized as ${\mathrm{Li}}^{+}$ cations. The internal bonding of ${[\mathrm{B}{\mathrm{H}}_{4}]}^{\ensuremath{-}}$ anions is primarily covalent. The high-frequency dielectric permittivity tensor ${\ensuremath{\epsilon}}_{\ensuremath{\infty}}$ is predicted as almost isotropic, but the static dielectric permittivity tensor ${\ensuremath{\epsilon}}_{0}$ as considerably anisotropic. The $\mathrm{\ensuremath{\Gamma}}$-phonon eigenmodes can be classified into three groups, namely, the librational modes involving the displacements of ${\mathrm{Li}}^{+}$ cations (less than $500\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$), and the internal B-H bending and stretching modes of ${[\mathrm{B}{\mathrm{H}}_{4}]}^{\ensuremath{-}}$ anions (around 1100 and $2300\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, respectively). The molecular approximation fairly reproduces the phonon frequencies in the latter two groups, implying the strong internal bonding of $\mathrm{B}{\mathrm{H}}_{4}$ complexes. The librational modes have significant contributions to the large anisotropies of ${\ensuremath{\epsilon}}_{0}$. The agreement of the heat of formation with the experimental value is reasonably good.

First-principles investigation of high-κdielectrics: Comparison between the silicates and oxides of hafnium and zirconium

Using density-functional theory, we investigate the structural, vibrational, and dielectric properties of Hf and Zr oxides and silicates which have drawn considerable attention as alternative high-kappa materials. For the silicates, we consider hafnon HfSiO4 and zircon ZrSiO4; while for the oxides, we study the cubic and tetragonal phases of HfO2 and ZrO2. Special emphasis is put on the analysis of the differences and similarities between Hf and Zr in these materials. In particular, we discuss the Born effective charge tensors, the phonon frequencies at the Gamma point of the Brillouin zone, and the dielectric permittivity tensors. Our study reveals very similar properties of Hf and Zr compounds, which are essentially related to the chemical homology of Hf and Zr.

First-principles study of structural, dynamical, and dielectric properties of A-La 2O 3

We have investigated the structural, dynamical, and dielectric properties of A-La 2O 3, within density-functional theory. The relaxed structural parameters are found to be in very good agreement with experimental data. Density-functional perturbation theory was used to calculate the zone-center phonon frequencies, Born effective charge tensors, and the dielectric permittivity tensors. The static permittivity constant is decomposed to its electronic component and the individual contribution of IR-active modes. It is found, for both the direction parallel to the trigonal axis and the direction perpendicular to it, that the ionic contribution to the static dielectric permittivity is mostly due to a single IR-active mode.

First-principles study of structural, dynamical, and dielectric properties of κ-Al 2O 3

We have performed a first-principles study of the structural, dynamical, and dielectric properties of κ-Al 2O 3. The relaxed structural parameters are found to be in excellent agreement with experimental data. Using density-functional perturbation theory, we obtain the Born effective charge tensors, the phonon frequencies at the center of the Brillouin zone, and the electronic and static dielectric permittivity tensors of κ-Al 2O 3. Using our calculated results of κ-Al 2O 3, together with the previous theoretical results of α-Al 2O 3 and available experimental data of amorphous Al 2O 3, we demonstrate the coordination dependence of ionic contribution to static dielectric constant of Al 2O 3.

Ab initio vibrational and dielectric properties of chalcopyrite CuInS 2

We have performed a first-principles study of structural, dynamical, and dielectric properties of the chalcopyrite semiconductor CuInS 2 . The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. Born effective charge tensors, dielectric permitivity tensors, the phonon frequencies at the Brillouin zone center and mode oscillator strengths are calculated using density functional perturbation theory. The calculated properties agree with infrared and Raman measurements.

Lattice dynamics and optical properties of yttrium oxysulfide

Lattice dynamics and optical properties of yttrium oxysulfide have been investigated with the combination of microscopic Raman scattering experiment and first-principles calculation. The Raman scattering experiment on our single crystals ensures an earlier Raman spectrum based on powdered samples. Ab initio calculation based on density-functional perturbation theory is performed to obtain the phonon modes in the first Brillouin zone, dielectric and Born effective charge tensors in the uniaxial crystal structure. A rigorous assignment of all the phonon modes at Γ-point is achieved, in agreement with the previous and present Raman experimental data. The calculated results also indicate the ambiguity of infra-red experimental results on oxysulfides. Since these physical values are related to the properties of polaron, our theoretical approach may be useful to understand optoelectronic processes such as scintillation.

Lattice dynamics and dielectric properties ofTiO2anatase: A first-principles study

Lattice vibrations and dielectric properties of the anatase phase of titanium dioxide are investigated from a theoretical perspective. A first-principles pseudopotential band calculation based on density-functional perturbation theory is performed to evaluate normal vibrations, dielectric tensors, and Born effective charges. The present theoretical predictions agree with experimental values overall. Born effective charge tensor elements appear anomalously large, as in the rutile phase, with a larger anisotropy of oxygen. Dielectric permittivity tensors are also discussed in comparison with those of rutile.

Ab initio vibrational and dielectric properties of the chalcopyriteCuInSe2

We have performed a first-principles study of structural, dynamical, and dielectric properties of the chalcopyrite semiconductor ${\mathrm{CuInSe}}_{2}.$ The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. Born effective charge tensors, dielectric permitivity tensors, the phonon frequencies at the Brillouin zone center, and mode oscillator strengths are calculated using density functional perturbation theory. The calculated properties agree with some of the infrared, Raman, and neutron measurements.

First-principles calculations on vibrational and dielectric properties of chalcopyriteCuGaS2

We have performed a first-principles study of structural, dynamical and dielectricproperties of chalcopyrite semiconductor CuGaS2. The calculations havebeen carried out within the local density functional approximation usingnorm-conserving pseudopotentials and a plane-wave basis. Born effective chargetensors, dielectric permittivity tensors, the phonon frequencies at the Brillouinzone centre and mode oscillator strengths are calculated using densityfunctional perturbation theory. The calculated properties help resolvethe source of some of the discrepancies in the experimental literature.

First-principles study of structural, vibrational, and lattice dielectric properties of hafnium oxide

Crystalline structures, zone-center phonon modes, and the related dielectric response of the three low-pressure phases of HfO2 have been investigated in density-functional theory using ultrasoft pseudopotentials and a plane-wave basis. The structures of low-pressure HfO2 polymorphs are carefully studied with both the local-density approximation (LDA) and the generalized gradient approximation (GGA). The fully relaxed structures obtained with either exchange-correlation scheme agree reasonably well with experiment, although LDA yields better overall agreement. After calculating the Born effective charge tensors and the force-constant matrices by finite-difference methods, the lattice dielectric susceptibility tensors for the three HfO2 phases are computed by decomposing the tensors into the contributions from individual infrared-active phonon modes.

Lattice dynamics and dielectric properties of yttrium oxysulfide

Lattice vibrations and optical properties of yttrium oxysulfide $({\mathrm{Y}}_{2}{\mathrm{O}}_{2}\mathrm{S})$ are investigated from a theoretical perspective. Density-functional perturbation theory based on first-principles pseudopotential method is employed to evaluate the phonon-band-structure, dielectric and Born effective charge tensors in a uniaxial crystal structure. A rigorous assignment of all the phonon modes is achieved. Microscopic Raman spectra on single crystals are also measured and found to be in good agreement with previous work on powdered samples. The present theoretical Raman frequencies are in fair agreement with the experimental data.

Phonons and lattice dielectric properties of zirconia

We have performed a first-principles study of the structural and vibrational properties of the three low-pressure (cubic, tetragonal, and especially monoclinic) phases of ZrO2, with special attention to the computation of the zone-center phonon modes and related dielectric properties. The calculations have been carried out within the local-density approximation using ultrasoft pseudopotentials and a plane-wave basis. The fully relaxed structural parameters are found to be in excellent agreement with experimental data and with previous theoretical work. The total-energy calculations correctly reproduce the energetics of the ZrO2 phases, and the calculated zone-center phonon frequencies yield good agreement with the infrared and Raman experimental frequencies in the monoclinic phase. The Born effective charge tensors are computed and, together with the mode eigenvectors, used to decompose the lattice dielectric susceptibility tensor into contributions arising from individual infrared-active phonon modes. This work has been partially motivated by the potential for ZrO2 to replace SiO2 as the gate-dielectric material in modern integrated-circuit technology.

First-principles Study of Electronic and Dielectric Properties of ZrO2 and HfO2

ABSTRACTUsing density-functional theory with ultrasoft pseudopotentials, we previously investigated the structural and electronic properties of the low-pressure (cubic, tetragonal, and monoclinic) phases of ZrO2 and HfO2, in order to elucidate phonon modes, Born effective charge tensors, and especially the lattice dielectric response in these phases. We now extend this previous work by carrying out similar calculations on the two high-pressure orthorhombic phases, and by providing density-of-states and band-gap information on all polymorphs. Our results show that the electronic structures and dielectric responses are strongly phase-dependent. In particular, the monoclinic phases of ZrO2 and HfO2 are found to have a strongly anisotropic dielectric tensor and a rather small orientational average () compared to the two other low-pressure phases. Our calculations show that is even smaller in the orthorhombic phases.

First-principles Study of Electronic and Dielectric Properties of ZrO2 and HfO2

ABSTRACTUsing density-functional theory with ultrasoft pseudopotentials, we previously investigated the structural and electronic properties of the low-pressure (cubic, tetragonal, and monoclinic) phases of ZrO2 and HfO2, in order to elucidate phonon modes, Born effective charge tensors, and especially the lattice dielectric response in these phases. We now extend this previous work by carrying out similar calculations on the two high-pressure orthorhombic phases, and by providing density-of-states and band-gap information on all polymorphs. Our results show that the electronic structures and dielectric responses are strongly phase-dependent. In particular, the monoclinic phases of ZrO2 and HfO2 are found to have a strongly anisotropic dielectric tensor and a rather small orientational average () compared to the two other low-pressure phases. Our calculations show that is even smaller in the orthorhombic phases.

First-principles study of dynamical and dielectric properties of tetragonal zirconia

Using the variational density-functional perturbation theory, we investigate the dynamical and dielectric properties of tetragonal zirconia (t-ZrO2). We obtain the phonon frequencies at the center of the Brillouin zone, the Born effective charge tensors, and the dielectric permittivity tensors. For all these quantities, a comparison is made with the related values in the cubic phase. The Born effective charge tensors are found to be quite anisotropic. The calculated phonon frequencies present a better agreement with the infrared and Raman experimental values than previous theoretical calculations. We propose symmetry assignments that solve the contradictions existing in the literature. The electronic and static dielectric permittivity constants are in relatively good agreement with experimental values. We perform a detailed analysis of the contribution of the various infrared-active modes to the static dielectric permittivity and explain its strong anisotropy.

Photoelasticity ofα-quartz from first principles

Using density-functional perturbation theory with a scissor correction, we compute the entire photoelastic tensor of $\ensuremath{\alpha}$-quartz. Its components, whose absolute values range between 0.047 and 0.29 are all described within 0.04. We also compute the Born effective charge tensor and present its variation with respect to strain, as well as the relative deformation potentials and the structural rearrangement caused by strain. Then, we discuss briefly the mechanisms involved in the photoelasticity of quartz.

First-principles study on structural, dielectric, and dynamical properties for three BN polytypes

We report the results of first-principles calculations on the structural properties (lattice constants and internal parameters), dielectric properties (macroscopic and static dielectric constants, and Born effective charge tensors), and dynamical properties $(\ensuremath{\Gamma}$-phonon frequencies) for the three polytypes of BN: the cubic zinc-blende structure $(c$-BN), the wurtzite structure $(w$-BN), and the hexagonal structure $(h$-BN). Our calculations were performed with the ultrasoft pseudopotential method and the linear response approach based on density-functional perturbation theory. By comparing the cohesive energies, we found that the c-BN structure is the most stable among the three polytypes at zero temperature. The computed equilibrium structural parameters, bulk moduli, and dielectric properties are in good agreement with the experimental data except for the lattice constant c of h-BN and the macroscopic dielectric constant along the c axis of h-BN. The $\ensuremath{\Gamma}$-phonon frequencies of c-BN and w-BN are close to each other. In order to distinguish c-BN and w-BN by Raman spectroscopy, it turns out that we should investigate the two Raman active ${E}_{2}$ modes that exist only in w-BN.

First-principles study of structural, electronic, dynamical, and dielectric properties of zircon

We investigate structural, electronic, dynamical, and dielectric properties of zircon $({\mathrm{ZrSiO}}_{4})$ within density-functional theory. The atomic structure is fully relaxed and the structural parameters are found to differ by less than 1.5% from the experimental data. The associated electronic band structure and density of states are also presented. Using density-functional perturbation theory, we obtain the phonon frequencies at the center of the Brillouin zone, the Born effective charge tensors, and the dielectric permittivity tensors. The calculated phonon frequencies agree with the infrared and Raman experimental values (rms relative deviations of 2.5%) when available, while the silent modes are predicted to range between 119.6 and $943.3{\mathrm{cm}}^{\ensuremath{-}1}.$ We compute the Born effective charge tensors, that are found to be quite anisotropic. The electronic and static dielectric permittivity are analyzed in detail. Their difference is mostly due to the lowest infrared-active mode, whose eigenvector corresponds to a distortion of the ${\mathrm{SiO}}_{4}$ tetrahedra with a displacement of Zr and O atoms in opposite directions.

Noncubic Behavior of Antiferromagnetic Transition-Metal Monoxides with the Rocksalt Structure

We give evidence that some nonmagnetic (i.e., spin-integrated) properties of the antiferromagnetic late transition-metal monoxides (MnO, FeO, CoO, NiO) are substantially noncubic below the N\'eel temperature even when assuming the ideal rocksalt structure for the ions. Our findings, which are at variance with the currently accepted picture, are based on ab initio and model calculations for the case study of MnO. The calculated zone-center optic phonon frequencies and Born effective charge tensor of this material show a significant magnetic-induced anisotropy.