Full-potential Local Orbitals Method Research Articles

Spin and orbital magnetism of exohedral fullerene doped with single transition metal atom (Sc-Ni): A relativistic density functional theory study

Relativistic density functional theory calculations have been implemented to study the structural configurations, electronic and magnetic properties of exohedral 3d transition metal atoms doping on C60 fullerene (TM-C60) by a full potential local orbital method. The calculated binding energies revealed that the TM-C60 molecules are energetically stable in all adsorption sites. We also found that the TM-doped exohedral C60 complexes are more reactive than pure C60 fullerene. The spin and orbital magnetic moments were also determined. We have indicated that in all of the five adsorption sites, exohedral TM-C60 molecules (except for Ni-C60) are magnetized. Our magnetic calculations show that the total spin magnetic moments of TM-C60 molecules mainly come from the TM atoms. We found that the spin magnetic moments of adsorbed TM atoms in exohedral doping C60 fullerene from Sc to Mn (HH adsorption site) and for Sc to Cr (HP and P adsorption sites) are greater than their free states. Our calculations suggest that exohedral doping 3d TM-C60 complexes can almost maintain spin magnetic moments. We have indicated that the magnetic properties of exohedral TM-C60 molecules change in the presence of spin–orbit coupling. Significant orbital contributions to magnetic moments are recognized in these configurations while the spin moments are unaffected. We found that Co in exohedral doping of C60 fullerene shows a robust orbital moment in all the five adsorption sites.

Uniaxial Strain and Optical properties of GaP Nanowires

The optical properties for wurtzite (WZ) Bulk GaP and GaP nanowires (GaP-NWs) in hexagonal(circular), triangular and square cross sectional are investigated by using full potential linear augmented plane waves and local orbitals (FP-LAPW-LO) method based on density functional theory (DFT). The wurtzite nanowires are investigated with diameters limited to ~27 oA. The optical functions as a function of photon energy have been investigated for unstrained bulk WZ-GaP and WZ-GaP-NWs in the first part. Finally, the optical functions are investigated for WZ-GaP-NWs by applying uniaxial strain from -5% to +5%. The effect of cross sectional variation in the area and shape of the NWs on the optical functions is clear when compared with bulk GaP. GaP-NWs kept real dielectric constant positive and refractive index close to vacuum value for a wider range of energy on the contrary of bulk GaP. It is found that the dielectric constants are slightly increased from the unstrained GaP-NWs values with strain increases. A shift in the threshold energy for toward higher energy as the strain changes from tensile to compressive. The refractive index shows a small change when passing from compressive toward tensile strain. It is found that GaP-NWs could play a role in solar cells structure and high speed electronic circuits.

Uniaxial Strain and Optical properties of GaP Nanowires

The optical properties for wurtzite (WZ) Bulk GaP and GaP nanowires (GaP-NWs) in hexagonal(circular), triangular and square cross sectional are investigated by using full potential linear augmented plane waves and local orbitals (FP-LAPW-LO) method based on density functional theory (DFT). The wurtzite nanowires are investigated with diameters limited to ~27 oA. The optical functions as a function of photon energy have been investigated for unstrained bulk WZ-GaP and WZ-GaP-NWs in the first part. Finally, the optical functions are investigated for WZ-GaP-NWs by applying uniaxial strain from -5% to +5%. The effect of cross sectional variation in the area and shape of the NWs on the optical functions is clear when compared with bulk GaP. GaP-NWs kept real dielectric constant positive and refractive index close to vacuum value for a wider range of energy on the contrary of bulk GaP. It is found that the dielectric constants are slightly increased from the unstrained GaP-NWs values with strain increases. A shift in the threshold energy for toward higher energy as the strain changes from tensile to compressive. The refractive index shows a small change when passing from compressive toward tensile strain. It is found that GaP-NWs could play a role in solar cells structure and high speed electronic circuits.

Theoretical investigation of spin–orbit coupling on structural, electronic and optical properties for CuAB2 (A = Sb, Bi; B = S, Se) compounds using Tran–Blaha-modified Becke–Johnson method: A first-principles approach

We investigate the structural, electronic and optical properties of CuAB2 (A = Sb, Bi; B = S, Se) compounds within density functional theory (DFT) using the full potential linear augmented plane wave plus local orbital (FP-LAPW + lo) method. For these total energy calculations, exchange correlation potentials, such as Perdew–Burke–Ernzerhof (PBE) and Tran–Blaha-modified Becke–Johnson (TB-mBJ) functionals, were executed with and without spin–orbit coupling (SOC). The CuSbSe2 compound shows a direct band gap nature and the other compounds of CuSbS2, CuBiS2 and CuBiSe2 show an indirect band gap nature. The calculated bandgap of these chalcogenides are in good agreement with the reported experimental results. The inclusion of SOC causes band degeneracies, which are confirmed from the electronic structure. The mobility of electrons and holes is higher in CuSbS2 and CuBiS2, whereas electron mobility decreases and hole mobility increases from the Sb-to the Bi-containing compounds. The calculated absorption coefficients of these compounds were greater than 105 cm−1, which make them suitable for optoelectronic applications.

The effect of Hubbard-like interaction on molecular magnetism of TM-coronene complex (TM = Fe and Co)

The adsorption of two transition metal adatoms, Fe and Co added to a coronene molecule were studied by means of a full potential local orbital method in the framework of relativistic density functional theory. A sequence of fixed spin moment calculations based on the Hubbard-like interaction (U) were carried out on the basis of the generalized gradient approximation (GGA) of the exchange–correlation functional. We found a transition from low-spin to high-spin state upon increasing the transition metal-coronene distance. Furthermore, the magnetism of both Fe-coronene and Co-coronene complexes revealed sensitivity to the magnitude of the U values. In our GGA+U (U = 2 eV) calculations, a low-spin ground state was found with in-plane magnetic anisotropy for both Fe-coronene and Co-coronene, whereas the GGA+U (U = 4 eV) calculations resulted in high-spin state with out-of-plane and in-plane magnetic anisotropy for Fe-coronene and Co-coronene, respectively.

DFT study of optoelectronic spectra of barium cadmium chalcogenides (Ba2CdX3, X = S, Se and Te)

AbstractDFT analyses of electronic and optical spectra of barium cadmium chalcogenides (Ba2CdX3, X = S, Se, Te) have been carried out. The study of electronic spectra has been made in terms of band structure and density of states using full potential linear augmented plane wave plus local orbital method. Band structure calculations have been carried out under the approximations PBE-GGA, PBE-Sol, LDA and TB-mBJ. Band structures of these materials show that Ba2CdS3, Ba2CdSe3and Ba2CdTe3crystals possess a band gap less than 1 eV, underestimated relative to the experimental/theoretical literature values. Optical spectra of these chalcogenides have been analyzed in terms of real and imaginary parts of dielectric function, reflectivity, refractive index, extinction coefficient, absorption coefficient, optical conductivity and electron energy loss. Optical results show large anisotropy along different directions. These results provide a physical basis of barium cadmium chalcogenides for potential application in optoelectronic devices.

The Surface Effect on the Thermoelectric Property of the [001] and [111] NaMgP Films: A DFT Study

Based on the density functional theory framework and full potential augmented plane waves plus local orbitals (FP-LAPW + lo) method with GGA-mBJ approximation, the electronic and thermoelectric (TE) properties of the NaMgP bulk and its films along the [001] and [111] directions have been calculated. The mechanical calculations including the energy–volume (E–V) diagram, elastic constants and phonon dispersion have been indicated the good stability of the NaMgP bulk in the static and dynamic view. The p-type semiconductor nature of this compound by 2.73 eV direct gap has been shown the suitable merit (ZT) parameter for TE applications of 50 K to 800 K temperature range. Based on the surface effect in the [001] and [111] films, the NaMg termination film of [001] film, MgP and NaP terminations of the [111] have the magnetic behavior with half-metallic and magnetic semiconductors, so, their TE behaviors were sensitive to the external magnetic field. The NaMg and MgP terminations have the high amount of the ZT at the 50 K and even that the room temperature for up-spin, which are suitable for power generators at higher temperatures. Also, the NaP termination has the big ZT at 50 K of the up-spin that is suitable for cooling technology.

The MN effect on Electronic, optical and thermoelectric properties of Ti2N graphene: by DFT

Electronic, optical and thermoelectric parameters of the Ti2N:Mn graphene sheet have been calculated by the density functional theory (DFT) framework. Our calculations were performed with full potential linear augmented plane waves plus local orbitals (FP-LAPW + lo) method and the exchange correlation potential was approximated by generalized gradient approximation (GGA). The Ti2N:Mn graphene sheet has anisotropic electronic behaviors indicating the magnetic property. The group velocity and effective mass in the valance band maximum (VBM) and conduction band minimum (CBM) have the high and low amounts, respectively. The optical response to the incident light in the infrared, visible area and ultraviolet edge are completely asymmetric while the optical responses at x and z directions are metallic and semiconductor, respectively. Thermoelectric parameters of Ti2N:Mn graphene have sensitivity to the external magnetic field, and the Seebeck (S) and merit coefficients (ZT) at spin up have great amounts in 150 K.

Spin-polarized optical properties of half-metallic binary XBi (X = Ca, Sr and Ba) compounds in zinc blende and wurtzite phases

In this work, we aim to study the spin-polarized optical properties of the non-transition metal-based binary compounds XBi (X = Ba, Sr and Ca) in the zinc blende and wurtzite phases. The calculations are performed by the developed full-potential augmented plane wave plus local orbitals (FP-L/APW + lo) method within the spin density functional theory. We used the Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation (PBE-GGA) and the recently modified Becke–Johnson potential (mBJ-GGA) to generate the exchange–correlation potential. The optical constants as the dielectric function, refractive index and extinction coefficient were calculated and discussed in detail. Our compounds are identified as potential candidates for spintronic applications and high-performance electronic devices, due to their possible half-metallic character. The interband transitions responsible for the structures in the spectra are specified. It is shown that the Bi-p states and (Ca, Sr, Ba)-d states play the major role in optical transitions as initial and final states.

Spin and orbital magnetism in phthalocyanine functionalized with 3d transition metals: A relativistic density functional theory study

The structural, magnetic, and electronic properties of 3d transition metal phthalocyanines, TMPc (TM = Sc-Ni, Cu), were studied by a full potential local orbital method in the framework of relativistic density functional theory. Binding energies, charge transfers, spin and orbital magnetic moments, and magnetic anisotropy energies were determined. Spin-orbit coupling in full relativistic regime together with orbital polarization correction to the exchange-correlation functional added a notable orbital contribution to magnetic moments of the individual 3d transition metals. In the presence of orbital polarization correction, significant in-plane orbital magnetic moments of 1.38 μB and 1.03 μB were found for vanadium atom in VPc and cobalt atom in CoPc, respectively. Besides, VPc showed planar magnetic anisotropy with 51.5 meV energy gain. Our calculations revealed that FePc has an out-of-plane easy axis.

Electronic structures and magnetic properties of 3d magnetic atoms adsorbed on olympicene molecule: A density functional theory study

The adsorption characteristics of transition metal (TM) adatoms on olympicene, a graphene-like molecule consisting of five rings of which four are benzene-like rings, are analyzed by means of first-principles calculations. The electronic structures and magnetic properties of 3d transition metals on olympicene were investigated in the framework of generalized-gradient approximation using relativistic density functional theory. Our calculations were based on full-potential local orbital (FPLO) method. Stable structure and total energies were obtained. Relaxed TM@Olympicene molecules, unlike the pure organic olympicene, were partially buckled. Binding energy calculations showed high stability for Ni@Olympicene whereas Mn did not bind to olympicene surface. Electronic charge transfers were consistent with Pauling electronegativities. The related HOMO-LUMO gaps decreased with respect to pure olympicene. Our calculated total and TM spin magnetic moments indicated that TM@Olympicene were strongly magnetized. Orbital polarization correction (OPC) were also used in order to get an upper estimation for orbital magnetic moment of all 3d atoms. Fe@Olympicene shows highest orbital moment of 0.18 μB. The Atoms in Molecules (AIM) approach was used to analyze the nature of TMC bonds in TM@Olympicene complexes. The results show the TMC bonds have a degree of covalency in their interactions.

A first principles study of the electronic structure, elastic and thermal properties of UB2

Uranium diboride (UB2) has been widely deployed for refractory use and is a proposed material for Accident Tolerant Fuel (ATF) due to its high thermal conductivity. However, the applicability of UB2 towards high temperature usage in a nuclear reactor requires the need to investigate the thermomechanical properties, and recent studies have failed in highlighting applicable properties. In this work, we present an in-depth theoretical outlook of the structural and thermophysical properties of UB2, including but not limited to elastic, electronic and thermal transport properties. These calculations were performed within the framework of Density Functional Theory (DFT) + U approach, using Quantum ESPRESSO (QE) code considering the addition of Coulomb correlations on the uranium atom. The phonon spectra and elastic constant analysis show the dynamic and mechanical stability of UB2 structure respectively. The electronic structure of UB2 was investigated using full potential linear augmented plane waves plus local orbitals method (FP-LAPW+lo) as implemented in WIEN2k code. The absence of a band gap in the total and partial density of states confirms the metallic nature while the valence electron density plot reveals the presence of covalent bond between adjacent B-B atoms. We predicted the lattice thermal conductivity (kL) by solving Boltzmann Transport Equation (BTE) using ShengBTE. The second order harmonic and third-order anharmonic interatomic force constants required as input to ShengBTE was calculated using the Density-functional perturbation theory (DFPT). However, we predicted the electronic thermal conductivity (kel) using Wiedemann-Franz law as implemented in Boltztrap code. We also show that the sound velocity along ‘a’ and ‘c’ axes exhibit high anisotropy, which accounts for the anisotropic thermal conductivity of UB2.

Metal mono-chalcogenides ZnX and CdX (X = S, Se and Te) monolayers: Chemical bond and optical interband transitions by first principles calculations

In this paper, we explore the structural, electronic and optical properties of ZnX and CdX (X=S, Se and Te) compounds in the two-dimensional (2D) graphene-like structure using the full potential augmented plane waves plus local orbitals (FP-APW+lo) method. Unlike their bulk phase, they are optically inactive because of their indirect band gap nature except CdS and ZnS. These two compounds maintain their direct band gap nature and hence are optically active. The static dielectric constants for these monolayers illustrate increasing trend with decrease in the band gap values. Furthermore, an acceptable description of electron transitions in these monolayers is accomplished according to the imaginary parts of the dielectric functions and absorption spectra in ZnS and CdS as examples of each group of CdX and ZnX. The results presented in this article revealed that ZnS and CdS in the 2D structure can be effectively used in optoelectronic devices such as solar cell materials and so forth.

Spin and orbital magnetism in XMg8(X=Sc-Ni): a relativistic density functional theory study

ABSTRACTThe electronic structure and magnetic properties in the transition metal atoms doped Mg8 metal cluster are investigated using a full potential local orbital method in the framework of relativistic density functional theory. We identify Fe@Mg8, Co@Mg8 and Ni@Mg8 with both high stability and large spin magnetic moment as magnetic superatoms. We have indicated that the spin-orbit coupling changes the magnetic properties of TM@Mg8 clusters. Significant orbital contributions to magnetic moments in these clusters are recognised while the spin moments are unaffected. We found that V and Co doped in Mg8 cluster show substantial orbital moments compared to the almost quenched orbital moments for the other 3d-transition metal adatoms embedded into the square antiprism Mg8 cluster . The orbital polarisation corrections were been used to adequate description of the orbital moment. We also found that these clusters follow superatomic picture.

Optoelectronic and thermoelectric properties of Zintl YLi3A2 (A = Sb, Bi) compounds through modified Becke–Johnson potential

In the present work, we investigate the structural, optoelectronic and thermoelectric properties of the YLi3X2 (X = Sb, Bi) compounds using the full potential augmented plane wave plus local orbital (FP-APW+lo) method. The exchange–correlation potential is treated with the generalized gradient approximation/local density approximation (GGA/LDA) and with the modified Becke–Johnson potential (TB-mBJ) in order to improve the electronic band structure calculations. In addition, the estimated ground state properties such as the lattice constants, external parameters, and bulk moduli agree well with the available experimental data. Our band structure calculations with GGA and LDA predict that both compounds have semimetallic behaviors. However, the band structure calculations with the GGA/TB-mBJ approximation indicate that the ground state of the YLi3Sb2 compound is semiconducting and has an estimated indirect band gap (Γ–L) of about 0.036 eV while the ground state of YLi3Bi2 compound is semimetallic. Conversely the LDA/TB-mBJ calculations indicate that both compounds exhibit semiconducting characters and have an indirect band gap (Γ–L) of about 0.15 eV and 0.081 eV for YLi3Sb and YLi3Bi2 respectively. Additionally, the optical properties reveal strong responses of the herein materials in the energy range between the IR and extreme UV regions. Thermoelectric properties such as thermal conductivity, electrical conductivity, Seebeck coefficient, and thermo power factors are also calculated.

Mulliken Occupation as the Indicator of Transition to Superconducting State in SrFe2As2and BaFe2As2

Basing on the ab initio calculations performed within full potential local orbital minimum basis method, the Mulliken occupation of the Sr 5s (n5s) and Ba 6p (n6p) states can serve as an indicator of transition to the superconducting state in doped SrFe2As2 and BaFe2As2 compounds where the iron was substituted with cobalt or in the pristine compounds under pressure. The estimated pressure, at which both compounds exhibit superconductivity based on Sr 5s and Ba 6p occupation is in good agreement with the recently published experimental data.

First principle study of magnetic and electronic properties of single X (X = Al, Si) atom added to small carbon clusters (C n X, n = 2–10)

In this paper, the magnetic and electronic properties of single aluminum and silicon atom added to small carbon clusters (C n X; X = Al, Si; n = 2–10) are studied in the framework of generalized-gradient approximation using density functional theory. The calculations were performed for linear, two dimensional and three dimensional clusters based on full-potential local-orbital (FPLO) method. The total energies, HOMO–LUMO energy gap and total magnetic moments of the most stable structures are presented in this work. The calculations show that C n Si clusters have more stability compared to C n Al clusters. In addition, our magnetic calculations were shown that the C n Al isomers are magnetic objects whereas C n Si clusters are nonmagnetic objects.

Investigating half-metallicity in PtXSb alloys (X=V, Mn, Cr, Co) at ambient and high pressure

The structural, electronic, magnetic and elastic properties of half-Heusler alloys PtMnSb, PtVSb, PtCrSb and PtCoSb are investigated using first-principles calculation based on Density Functional Theory DFT. The Full Potential local Orbital (FPLO) method, within the General Gradient Approximation (GGA) and Local Spin Density Approximation (LSDA), have been used. The calculated structural, electronic and magnetic properties are in good agreement with available experimental and theoretical data. Using GGA approximation, only PtVSb shows a half-metallic behavior with a spin-down band gap and total magnetic moment of 0.802eV and 2µB respectively. Both of PtVSb and PtMnSb alloys are half-metallic with spin-down band gaps of 0.925eV and 0.832eV and magnetic moments of 2µB and 4µB respectively using LSDA approximation. The bulk modulus and its first pressure-derivative of these alloys are calculated using the modified Birch–Murnaghan equation of state (EOS). The effect of pressure on the lattice constant, energy gap and bulk modulus is investigated. Under pressure, PtMnSb and PtCrSb turn into half-metallic alloys at nearly 6GPa and 27GPa respectively using GGA approximation.

A first-principles study on structural, thermodynamics and elastic properties of XNBa3 (X = As, Sb) under pressure and temperature effect

Abstract The full potential augmented plane wave plus local orbital (FP-LAPW + lo) method using the generalized-gradient approximation within the framework of density functional theory is applied to the study of the lattice constant, bulk modulus, pressure derivative of the bulk modulus and elastic constants under high pressure of antiperovskite XNBa3. The Young's and shear modulus, Poisson ratio, have also been calculated. Through quasi-harmonic approximation, the temperature effect on the thermodynamic quantities in the whole pressure range from 0 to 30 GPa and temperature range from 0 to 1200 K.

Electrical resistivity of the heavy-fermion-filled cage compoundCe3M4Sn13(M=Co,Rh,Ru)under high pressure

The effect of pressure on electrical resistivity of heavy-fermion compounds ${\mathrm{Ce}}_{3}{M}_{4}{\mathrm{Sn}}_{13}$, where $M=\mathrm{Co}$, Rh, Ru, and the ${\mathrm{La}}_{3}{M}_{4}{\mathrm{Sn}}_{13}$ counterparts is studied in the framework of the fully relativistic full potential local orbital method. The experiment shows that the electrical resistivity of ${\mathrm{Ce}}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$ and ${\mathrm{Ce}}_{3}{\mathrm{Rh}}_{4}{\mathrm{Sn}}_{13}$ increases with pressure, a similar pressure effect is obtained for isostructural La-based reference metals, while opposite behaviors under pressure are documented for ${\mathrm{Ce}}_{3}{\mathrm{Ru}}_{4}{\mathrm{Sn}}_{13}$ and ${\mathrm{La}}_{3}{\mathrm{Ru}}_{4}{\mathrm{Sn}}_{13}$. The contrasting pressure dependent effects of ${\mathrm{Ce}}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$ and ${\mathrm{Ce}}_{3}{\mathrm{Ru}}_{4}{\mathrm{Sn}}_{13}$ are discussed. In order to clarify the various phenomena the band-structure calculations under applied pressure were performed. Here, we show that the resistivity increase with pressure arises from the formation of interband distances at the Fermi level in ${\mathrm{Ce}}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$, this pseudo-gap-like effect is also pressure dependent, while in ${\mathrm{Ce}}_{3}{\mathrm{Ru}}_{4}{\mathrm{Sn}}_{13}$ the opposite change of resistivity results from the suppression of spin fluctuations under pressure.