arXiv subjects

Sudhir K. Pandey

Publications and source records attributed to Sudhir K. Pandey.

At least 37 records · Page 2Linked to original sources

arXiv2024

PH-NODE: A DFPT and finite displacement supercell based python code for searching nodes in topological phononic materials

Exploring the topological physics of phonons is fundamentally important for understanding various practical applications. Here, we present a density-functional perturbation theory and finite displacement supercell based Python 3 software package called PH-NODE for efficiently computing phonon nodes present in real material through a first-principle approach. The present version of the code is interfaced with the WIEN2k, Elk, and ABINIT packages. In order to benchmark the code, four different types of materials are considered, which include (i) FeSi, a well-known double-Weyl point; (ii) LiCaAs, a half-Heusler single-type-I Weyl topological phonon (TP); and (iii) ScZn, coexisting nodal-line and nodal-ring TPs; (iv) TiS, six pairs of bulk Weyl nodes. In FeSi, the node points are found at $Γ$(0, 0, 0) and R(0.5, 0.5, 0.5) high symmetric points. Also, there are 21 energy values at which the node points are situated, corresponding to the full Brillouin Zone. For LiCaAs, the previously reported literature claims that there is a node point along the W-X high symmetry direction between the highest longitudinal acoustic and the lowest transverse optical branch, while in our DFT calculations, a gap of 0.17 meV is found. Furthermore, ScZn hosts six nodal-ring TPs phonons at the boundary planes of the Brillouin Zone in the vicinity of the M high-symmetric point. In addition to this, straight-line TPs are also found along the $Γ$-X and $Γ$-R high symmetric directions. Moreover, for TiS, six weyl node points (WP1, WP2, WP3, WP4, WP5 and WP6) are found along H-K high-symmetric direction. The results obtained from the PH-NODE code are in good agreement with the experimentally and theoretically reported data for each material.

cond-mat.mtrl-sci↗

arXiv2024

Observation of correlation induced metal to half-metal phase transition and large orbital moment in $\mathrm{Sr_2CoO_4}$

We present a detailed mean-field study to address the fundamental discrepancy in the ground state magnetization of $\mathrm{Sr_{2}CoO_{4}}$ (SCO). In contrast to the ferromagnetic metallic ground state obtained from density functional theory (DFT), DFT+$U$ gives three ferromagnetic solutions converging to integer moment values (1, 2 \& 3 $μ_B$/f.u) over a range of $U$. Interestingly, two of the solutions are found to exhibit half-metallicity with correspondingly $S$=1/2 and S=3/2 spin states. The half-metallic ferromagnetic state with $S$=3/2 is found to be the ground state solution for SCO. Co atoms show a large deviation from the formal +4 oxidation state indicating the presence of strong covalency effects. Our results suggest a plausible metal to half-metal phase transition around $U$($J$)=4.4(1.16) eV. The Fermi surface study shows gradual collapse in states leading to half-metallicity suggesting \textit{\textbf{k}}-dependence of effective $U$ around the critical region. Surprisingly, in the presence of spin-orbit coupling (SOC), unexpectedly large orbital moment ($L_{z}$=0.6) is noted in SCO putting it among the class of 3$d$ based transition metal compounds exhibiting pronounced orbital magnetization. The calculations give large magnetocrystalline anisotropy energy (MAE) of $\sim$48 meV. Large values of orbital magnetic moment contribution and MAE, in the presence of strong correlation effects, provide a better interpretation of experimental magnetization observed in SCO.

cond-mat.str-el↗

arXiv2023

Exploring the effect of strong electronic correlations in Seebeck Coefficient of the NdCoO3 compound : Using experimental and DFT+U approach

The presence of complexity in the electronic structure of strongly correlated electron system NdCoO$_3$ (NCO) have sparked interest in the investigation of its physical properties. Here, we study the the Seebeck coefficient ($α$) of NCO by using the combined experimental and DFT+$U$ based methods. The experimentally measured $α$ is found to be $\sim$ 444 $μV/K$ at 300 K, which decreases to 109.8 $μV/K$ at 600 K. In order to understand the measured $α$, we have calculated the PDOS and band structure of the NCO. Furthermore, the calculated occupancy of 6.4 for Co $3d$ orbitals and presence of large unoccupied O $2p$ states indicate the covalent nature of the bonding. Apart from this, the maximum effective mass is found to be 36.75 (28.13) for the spin-up (dn) channel in conduction band indicates the n-type behaviour of the compound in contrast to our experimentally observed p-type behaviour. While, the calculated $α$ at the temperature-dependent chemical potential ($μ$) at 300 K shows the p-type behaviour of the compound. Fairly good agreement is seen between the calculated and measured values of $α$ at U$_f$$_f$ = 5.5 eV and U$_d$$_d$ = 2.7 eV. The maximum power factor (PF) is found to be 47.6 (114.4) $\times$ $10^1$$^4 $ $μ$$W$$K^-$$^2$$cm^-$$^1$$s^-$$^1$ at 1100 K, which corresponds to p (n)-type doping of $\sim$ 1.4 (0.7) $\times$ 10$^2$$^1$ cm$^-$$^3$. This study suggests the importance of strong on-site electron correlation in understanding the thermoelectric property of the compound.

cond-mat.mtrl-sci↗

arXiv2023

Ab initio investigation of the lattice dynamics and thermophysical properties of BCC Vanadium and Niobium

In the present work, we have performed the phonon dispersion calculations of body-centered cubic Vanadium (V) and Niobium (Nb) with the supercell approach using different supercell size. Using DFT method, the calculated phonon spectra of V and Nb are found to be in a good agreement with the available experimental data. Our calculated results show a \enquote{dip}-like feature in the longitudinal acoustic phonon mode along the $Γ$-H high symmetric path for both transition metals in the case of supercell size 4$\times$4$\times$4. However, in supercell size 2$\times$2$\times$2 and 3$\times$3$\times$3, the \enquote{dip}-like feature is not clearly visible. In addition to this, thermodynamical properties are also computed, which compare well with the experimental data. Apart from this, the phonon lifetime due to electron-phonon interactions ($τ_{\rm{eph}}^{\rm{ph}}$) and phonon-phonon interactions ($τ_{\rm{ph}}^{\rm{ph}}$) are calculated. The effect of phonon-phonon interactions (PPI) is studied by computing the average phonon lifetime for all acoustic branches. The value of $τ_{\rm{eph}}^{\rm{ph}}$ of V (Nb) is found to be 23.16 (24.70)$\times 10^{-15}$ s at $100$ K, which gets decreased to 1.51 (1.85)$\times 10^{-15}$ s at 1000 K. The $τ_{\rm{ph}}^{\rm{ph}}$ of V (Nb) is found to be 8.59 (18.09)$\times 10^{-12}$ and 0.83 (1.76)$\times 10^{-12}$ s at 100 and 1000 K, respectively. Nextly, the lattice thermal conductivity is computed using linearized phonon Boltzmann equation. The present work suggests that studying the variation of phonon dispersion with supercell size is crucial for understanding the phonon properties of solids accurately.

cond-mat.mtrl-sci↗

arXiv2023

Investigating the effect of electronic correlation on transport properties and phononic states of Vanadium

In the present work, we have tried to investigate the importance of electronic correlation on transport properties and phononic states of Vanadium (V). The temperature-dependent electrical resistivity ($ρ$) and electronic part of thermal conductivity ($κ_e$) due to electron-electron interactions (EEIs) and electron-phonon interactions (EPIs) are computed. The values of $ρ$ due to EEIs are found to be extremely small in comparison to $ρ$ due to EPIs. For instance, at 300 K, the calculated value of $ρ$ due to EEIs (EPIs) is $\sim$ 0.859$\times10^{-3}$ ($\sim$ 0.20) $μΩ$m. The magnitudes of $κ_e$ due to EPIs are found to be in good agreement with the experimental results. These observations indicate the negligible importance of EEIs to these quantities for V. However, at 300 K, the value of Seebeck coefficient ($S$) at DFT+DMFT level ($\sim$ -0.547 $μ$VK$^{-1}$) is found to be entirely different than at DFT level ($\sim 7.401$ $μ$VK$^{-1}$). Also, the DFT+DMFT value of $S$ at 300 K is in good match with the available experimental data (-1.06 $μ$VK$^{-1}$, 1.0 $μ$VK$^{-1}$). Apart from this, the study of phononic states at DFT and DFT+DMFT level is performed. The obtained phononic band structure and phonon DOS at DFT+DMFT differ to a good extent from that at DFT. The maximum energy of phononic state obtained at DFT (DFT+DMFT) is $\sim$ 33.83 ($\sim$ 35.15) meV, where the result of DFT+DMFT is obtained more closer to the experimental data (35.15, 36.98 & 41.77 meV). These results highlight the importance of electronic correlation on $S$ & phononic states of simple correlated V metal.

cond-mat.str-el↗

arXiv2023

Existence of nodal-arc and its evolution into Weyl-nodes in the presence of spin-orbit coupling in TaAs & TaP

In this work, we report the existence of nodal-arc, which acts as the building block of all the nodal-rings in TaAs & TaP. This nodal-arc is found to be capable of generating all the nodal-rings in these materials upon the application of space-group symmetry operations including time-reversal symmetry. The arcs are obtained to be dispersive with the energy spread of $\sim$109 ($\sim$204) meV in TaAs (TaP). Also, the orbitals leading to bands-inversion and thus the formation of nodal-arcs are found to be Ta-5d & As-4p (P-3p) in TaAs (TaP). The area of nodal-rings is found to be highly sensitive to the change in hybridization-strength, where the increase in hybridization-strength leads to the decrease in the area of nodal-rings. In the presence of spin-orbit coupling (SOC), all the points on these arcs get gaped-up and two pairs of Weyl-nodes are found to evolve from them. Out of the two pair, one is found to be situated close to the joining point of the two arcs forming a ring. This causes the evolution of each nodal-ring into three pairs of Weyl-nodes. The coordinates of these Weyl-nodes are found to be robust to the increase in SOC-strength from $\sim$ 0.7-3.5 eV. All the results are obtained at the first-principle level. This work provides a clear picture of the existence of nodal-arc due to accidental degeneracy and its evolution into Weyl-nodes under the effect of SOC.

cond-mat.mes-hall↗

arXiv2023

Lattice dynamics related properties of Nickel: A comparative DFT and DFT+U study

The simultaneous influence of electronic correlations and magnetic ordering on the theoretical estimation of phonons and related properties of Ni is investigated. The work includes a comparative DFT and DFT+U study, where on-site Coulomb interaction parameter for 3$d$ electrons, $U$($U_{full}$)= 0.516 eV obatined from constarined random phase approximation (cRPA) calculations, is considered for DFT+U calculations. The analysis of phonon frequency estimates along high symmetric k-directions and sampled full-BZ (Brillouin zone) using Frozen phonon displacement method suggests the importance of both on-site Coulomb correlations and magnetism to account for the experimental frequencies. Further, prominent role of both the aspects is observed in the derived thermodynamic properties - Free-energy, specific heat \& entropy, within quasi-harmonic approximation (QHA) specially at high temperatures. The temperature dependent evaluation of thermal expansion coefficient($α$) and phonon density of states is performed together with the equilibrium elastic constants. The results obtained for Ni, suggest the significance of electronic energy correction due to both on-site Coulomb correlations and magnetic phase incorporation, to account for realistic description of experimental findings. This study realizes the inevitable role of correlation effects in studying the phononic properties of a correlated transition metal, hence directing a way to explore various other correlated electron systems for their lattice dynamics.

cond-mat.str-el↗

arXiv2022

PY-Nodes: An ab-initio python code for searching nodes in a material using Nelder-Mead's simplex approach

With the discovery of topological semimetals, it has been found that the band touching points near the Fermi level are of great importance. They give rise to many exciting phenomena in these materials. Moreover, these points, commonly known as nodes, are related to several properties of these semimetals. Thus, the proper estimation of their coordinates is extremely needed for better understanding of the properties of these materials. We have designed a Python 3 based code named PY-Nodes for efficiently finding the nodes present in a given material using first-principle approach. The present version of the code is interfaced with the WIEN2k package. For benchmarking the code, it has been tested on some famous materials which possess characteristic nodes. These include - TaAs, a well-known Weyl semimetal, Na$_3$Bi, which is categorized as Dirac semimetal, CaAgAs, classified as a nodal-line semimetal and YAuPb, which is claimed to be non-trivial topological semimetal. In case of TaAs, 24 nodes are obtained from our calculations. On computing their chiralities, it is found that 12 pairs of nodes having equal and opposite chirality are obtained. Furthermore, for Na$_3$Bi, a pair of nodes are obtained on the either side of $Γ$-point in the $\boldsymbol{k_3}$ direction. In case of CaAgAs, several nodes are obtained in the $k_z$=0 plane. These nodes, when plotted in the $k_x$-$k_y$ plane, form a closed loop which is generally referred to as nodal-line. Finally, in the case of YAuPb, large number of nodes are obtained in the vicinity of $Γ$-point. The results obtained for these materials are in good match with the previous works carried out by different research groups. This assures the reliability and the efficiency of the PY-Nodes code for estimating the nodes present in a given material.

cond-mat.mtrl-sci↗

arXiv2022

Possible realization of three-dimensional quantum spin liquid behavior in HoVO4

The study of geometrically frustrated magnetic systems with unusual crystal field ground states offers a possibility of realizing the new aspects of physics of disordered systems. In this study, we report our results of structural, magnetic susceptibility, heat capacity measurements, along with density functional theory calculations on HoVO4; a compound in which the presence of a distorted kind of HoO8 polyhedral leads to multiple magnetic interaction paths. The observed broad maximum below 10 K in the temperature response of DC susceptibility curves implies the presence of short-range correlations. AC susceptibility rules out the possibility of any kind of spin freezing. Temperature dependent heat capacity measurement at zero field indicate towards the absence of long-range ordering, along with the presence of a broad maximum centered around 14 K. The residual heat capacity exhibits a characteristic power-law (Tα) behavior with the exponent α nearly equal to 2, which is analogous to that observed for other 3D quantum spin liquid systems. The density functional theory calculations signify the presence of dominant second and third nearest neighbor interactions, which in turn lead to magnetic frustration in our system. Our investigations suggest that HoVO4 can be a candidate for realizing a 3D quantum spin liquid state.

cond-mat.str-el↗

arXiv2022

First-principles evidence of type-II Weyl phonons in rock-salt Tin Chalcogenides (SnS, SnSe & SnTe) materials

Recent studies on different topological materials in condensed matter physics have provided the evidence of topological nature for bosonic particle like phonons by performing various theoretical calculations and experimental observations. Here, the topological behaviours of phonons of SnS, SnSe and SnTe materials in rock-salt structure are investigated using $ab$-$initio$ methodology. For all these materials, the tilted linear band touching is observed along with the presence of band inversion in direction X-W. The topological point in phonon dispersion curve along X-W direction is found to be $\sim$2.83, $\sim$2.46 and $\sim$2.51 THz for SnS, SnSe and SnTe, respectively. The calculated numbers of Weyl points (WPs) is estimated to be 56, 24 and 54 for SnS, SnSe and SnTe, respectively. These WPs have shown conserved Chiral charges for all corresponding materials. The surface local density of states is computed for these compounds, where the surface arc is clearly seen. In case of SnS, the surface arc is found at 2.0 - 2.2 THz energy region. Also, the isofrequency surface states are investigated to observe the presence of Fermi arc for SnX (X = S, Se, Te). The present first-principles calculation predicts that SnS, SnSe and SnTe show type-II Weyl phononic behaviour along with evidence of topological phononic surface states.

cond-mat.mtrl-sci↗

arXiv2022

Evidence of phase stability, topological phonon and temperature-induced topological phase transition in rocksalt SnS and SnSe

Both SnS and SnSe have been experimentally and theoretically confirmed as topological crystalline insulators in native rocksalt structure. Here, phononic structure, thermodynamical properties and temperature dependent electron-phonon interaction (EPI) have investigated for both the materials in rocksalt phase. Previously performed theoretical studies have predicted the phase instability of SnS in this crystal structure at ambient condition. But, after a detailed study performing on the phonon calculation of SnS, we have predicted the phase stability of SnS with considering the Sn 4$p$ orbitals as valence states in $ab-initio$ calculation. The importance of long range Coulomb forces along with the themodynamical properties are also described in detailed for both materials. The preliminary evidence of topological phonon is found along X-W direction, where the linear band touching is observed as compared to type II Weyl phononic material ZnSe. The topological phase transition is seen for these materials due to EPI, where non-linear temperature dependent bandgap is estimated. The predicted value of transition temperature for SnS (SnSe) is found to be $\sim$700 K, where after this temperature the non-trivial to trivial topological phase is seen. The strength of EPI shows more stronger impact on the electronic structure of SnS than SnSe material. The reason of non-linear behaviour of bandgap with rise in temperature is discussed with the help of temperature dependent linewidths and lineshifts of conduction band and valence band due to EPI. The present study reveals the phase stability of SnS along with the comparative study of thermal effect on EPI of SnS and SnSe. Further, the possibility of temperature induced topological phase transition provides one of important behaviour to apply these two materials for device making application.

cond-mat.mtrl-sci↗

arXiv2022

Density functional study of thermodynamic properties, thermal expansion and lattice thermal conductivity of Fe$_{2}$VAl at high temperature region

Here, we present the phonon calculations for thermodynamic properties, thermal expansion and lattice thermal conductivity of Fe$_{2}$VAl in the temperature range of $300-800$ K and compared with existing experiment. Phonon dispersion is computed using finite displacement method and supercell approach. The positive frequencies of all the phonon modes indicate the mechanical stability of the compound. The specific heat at constant volume and Helmholtz free energy are calculated under harmonic approximation, while calculation of thermal expansion is done under quasi-harmonic approximation. Lattice thermal conductivity ($κ_{L}$) is calculated using first-principle anharmonic lattice dynamics calculations. The zero-point energy and Debye temperature are computed as $\sim$21 kJ/mol and 638 K, respectively. The calculated thermal expansions are found to be $\sim$6.3 $\times$ 10$^{-6}$ K$^{-1}$ and $\sim$7.2 $\times$ 10$^{-6}$ K$^{-1}$ at 300 and 800 K, respectively. A significant deviation between calculated ($\sim$48.6 W/m-K) and experimental ($\sim$22.8 W/m-K) values of $κ_{L}$ are observed at 300 K. But, as the temperature increases, the calculated and experimental $κ_{L}$ come closer with the corresponding values of $\sim$18.2 W/m-K and $\sim$11.0 W/m-K at 800. The possible reasons for the deviation of $κ_{L}$ are addressed. The temperature dependent of phonon lifetime is computed in order to understand the feature of $κ_{L}$. Present study suggests that DFT based phononic calculations provide reasonably good explanations of available experimental phonon related properties of Fe$_{2}$VAl in the high temperature range of $300-800$ K.

cond-mat.mtrl-sci↗

arXiv2022

Thermoelectric properties of Fe$_{2}$VAl at high temperature region: A combined experimental and theoretical study

Heusler type compounds have long been recognized as potential thermoelectric (TE) materials. Here, the experimentally observed TE properties of Fe$_{2}$VAl are understood through electronic structure calculations in the temperature range of $300-800$ K. The observed value of $S$ is $\sim-$138 $μ$V/K at 300 K. Then, the $|S|$ decreases with increase in temperature up to the highest temperature with the value of $\sim-$18 $μ$V/K at 800 K. The negative sign of $S$ in the full temperature window signifies the dominating $n$-type character of the compound. The temperature dependent of electrical conductivity, $σ$ (thermal conductivity, $κ$) exhibits the increasing (decreasing) trend with the values of $\sim$1.2 $\times$ 10$^{5}$ $Ω^{-1}$m$^{-1}$ ($\sim$23.7 W/m-K) and $\sim$2.2 $\times$ 10$^{5}$ $Ω^{-1}$m$^{-1}$ ($\sim$15.3 W/m-K) at 300 K and 800 K, respectively. In order to understand these transport properties, the DFT based semi-classical Boltzmann theory is used. The contributions of multi-band electron and hole pockets are found to be mainly responsible for the temperature dependent trend of these properties. The decrement of $|S|$ and increment of $σ/τ$ $\&$ $κ_{e}/τ$ ($τ$ is relaxation time) with temperature is directly related with the contribution of multiple hole pockets. Present study suggests that DFT based electronic calculations provide reasonably good explanations of experimental TE properties of Fe$_{2}$VAl in the high temperature range of $300-800$ K.

cond-mat.mtrl-sci↗

arXiv2022

Exploring temperature dependent electron-electron interaction of topological crystalline insulators (SnS and SnSe) within Matsubara-time domain

Both experimental and theoretical studies show non-trivial topological behaviour in native rocksalt phase for SnS and SnSe and categorize these materials in topological crystalline insulators. Here, the detailed electronic structures studies of SnS and SnSe in the rocksalt phase are carried out using many-body $GW$ based theory and density functional theory both for ground states and temperature dependent excited states. The estimated values of fundamental direct bandgaps around L-point using $G_0W_0$ (mBJ) are $\sim$0.27 ($\sim$0.13) eV and $\sim$0.37 ($\sim$0.17) eV for SnS and SnSe, respectively. The strength of hybridization between Sn 5$p$ and S 3$p$ (Se 4$p$) orbitals for SnS (SnSe) shows strong k-dependence. The behaviour of $\overline{W}$ ($ω$), which is the averaged value of diagonal matrix elements of fully screened Coulomb interaction, suggests to use full-$GW$ method for exploring the excited states because the correlation effects within these two materials are relatively weak. The temperature dependent electronic structure calculations for SnS and SnSe provide linearly decreasing behaviour of bandgaps with rise in temperatures. The existence of collective excitation of quasiparticles in form of plasmon is predicted for these compounds, where the estimated values of plasmon frequency are $\sim$9.5 eV and $\sim$9.3 eV for SnS and SnSe, respectively. The imaginary part of self-energy and mass renormalization factor ($Z_\textbf{k}(ω)$) due to electron-electron interaction (EEI) are also calculated along W-L-$Γ$ direction for both the materials. The present comparative study reveals that the behaviour of temperature dependent EEI for SnS and SnSe are the almost same and EEI is important for high temperature transport properties.

cond-mat.str-el↗

arXiv2021

First-principles phonon calculations for lattice dynamics, thermal expansion and lattice thermal conductivity of CoSi at high temperature region

This study presents the first-principles phonon calculations to understand the experimental thermal expansion ($α(T)$) and lattice thermal conductivity ($κ_{L}$) of CoSi at high temperature region. Phonon dispersion is computed using finite displacement method and supercell approach by taking the equilibrium crystal structures obtained from DFT. The calculation of $α(T)$ is done under quasi-harmonic approximation. The $κ_{L}$ is calculated using first-principle anharmonic lattice dynamics calculations under single-mode relaxation time approximation. Calculated $α(T)$ in the temperature range $0-1300$ K gives the good match with existing experimental data. The calculated value of $κ_{L}$ ($\sim$8.0 W/m-K) at 300 K is found to be in good agreement with the experimental value of $\sim$8.3 W/m-K. The temperature dependent of phonon lifetime due to phonon-phonon interaction is calculated to understand the behaviour of $κ_{L}$. Present study suggests that ground state phonon dispersion obtained from DFT based methods gives reasonably good explanation of experimental $α(T)$ and $κ_{L}$.

cond-mat.mtrl-sci↗

arXiv2021

Experimental and computational approaches to study the high temperature thermoelectric properties of novel topological semimetal CoSi

Here, we study the thermoelectric properties of topological semimetal CoSi in the temperature range $300-800$ K by using combined experimental and density functional theory (DFT) based methods. CoSi is synthesized using arc melting technique and the Rietveld refinement gives the lattice parameters of a = b = c = 4.445 Å. The measured values of Seebeck coefficient (S) shows the non-monotonic behaviour in the studied temperature range with the value of $\sim-$81 $μ$V/K at room temperature. The $|S|$ first increases till 560 K ($\sim-$93 $μ$V/K) and then decreases up to 800 K ($\sim-$84 $μ$V/K) indicating the dominating n-type behaviour in the full temperature range. The electrical conductivity, $σ$ (thermal conductivity, $κ$) shows the monotonic decreasing (increasing) behaviour with the values of $\sim$5.2$\times 10^{5}$ (12.1 W/m-K) and $\sim$3.6$\times 10^{5}$ (14.2 W/m-K) $Ω^{-1}m^{-1}$ at 300 K and 800 K, respectively. The $κ$ exhibits the temperature dependency as, $κ\propto T^{0.16}$. The DFT based Boltzmann transport theory is used to understand these behaviour. The multi-band electron and hole pockets appear to be mainly responsible for deciding the temperature dependent transport behaviour. Specifically, the decrease in the $|S|$ above 560 K and change in the slope of $σ$ around 450 K are due to the contribution of thermally generated charge carriers from the hole pockets. The temperature dependent relaxation time is computed which shows temperature dependency of $1/T^{0.35}$. Present study suggests that electronic band-structure obtained from DFT provides reasonably good estimate of the transport coefficients of CoSi in the high temperature region of $300-800$ K.

cond-mat.mtrl-sci↗

arXiv2021

TRACK: A python code for calculating the transport properties of correlated electron systems using Kubo formalism

Exploring the transport properties of different materials brings new avenue for basic understanding of emergent phenomena and practical applications in many different fields. Here, we report a program named as TRACK (TRAnsport properties for Correlated materials using Kubo formalism) which is written in Python 3 for calculating temperature dependent electrical conductivity, electronic part of thermal conductivity, Seebeck coefficient and Lorenz number. In this code, Kubo linear-response formalism is utilized for computing these parameters using both interacting and non-interacting electronic structure methods. The formula for transport coefficients is accordingly modified to obtain the transport parameters under relaxation time approximation using band-theory. The basic inputs of this program are the structural information, dense k-points sampling in the irreducible part of the Brillouin zone and the information of velocity matrix elements, which can be calculated using third-party ab-initio package. TRACK is expected to calculate the transport properties of different class of materials. The code has been benchmarked by performing calculation on three different types of materials namely Vanadium (V), FeSi and LaCoO$_3$, which are metal, semiconductor and Mott insulator, respectively. The temperature dependent behaviour of the transport coefficients for these materials show fairly good agreement with the corresponding experimental data.

cond-mat.str-el↗

arXiv2021

Understanding the Seebeck coefficient of LaNiO3 compound in the temperature range 300-620 K

Transition metal oxides have been attracted much attention in thermoelectric community from the last few decades. In the present work, we have synthesized LaNiO$_{3}$ by a simple solution combustion process. To analyze the crystal structure and structural parameters we have used Rietveld refinement method wherein FullProf software is employed. The room temperature x-ray diffraction indicates the trigonal structure with space group $R \, \overline{3} \, c$ (No. 167). The refined values of lattice parameters are a = b = 5.4615 Å\, $\&$ c = 13.1777 Å. Temperature dependent Seebeck coefficient (S) of this compound has been investigated by using experimental and computational tools. The measurement of S is conducted in the temperature range $300-620$ K. The measured values of S in the entire temperature range have negative sign that indicates \textit{n}-type character of the compound. The value of S is found to be $\sim$ $-$8 $μ$V/K at 300 K and at 620 K this value is $\sim$ $-$12 $μ$V/K. The electronic structure calculation is carried out using DFT+\textit{U} method due to having strong correlation in LaNiO$_{3}$. The calculation predicts the metallic ground state of the compound. Temperature dependent S is calculated using BoltzTraP package and compared with experiment. The best matching between experimental and calculated values of S is observed when self-interaction correction is employed as double counting correction in spin-polarized DFT + \textit{U} (= 1 eV) calculation. Based on the computational results maximum power factors are also calculated for \textit{p}-type and \textit{n}-type doping of this compound.

cond-mat.mtrl-sci↗