Full-potential Approach Research Articles

Structural, electronic and optical characterization of thin film CH3 NH3 PbX3 (X =I and Br) compared to first-principles calculations

The present work reports the theoretical and experimental studies of structural, the electronic and optical properties of the CH3NH3PbX3(X=I and Br)(MAPX) thin film as precursor materials for perovskite based optoelectronic devices. X-ray diffraction, photoluminescence, atomic force microscopy and ultraviolet–visible–near infrared spectrophotometry were used to obtain, respectively, structural, morphological and optical properties of deposited films. This research used density functional theory (DFT) computation, using the GGA-PBE approximation, to investigate in depth the properties of CH3NH3PbX3(X=I and Br) hybrid perovskites. The X-ray diffraction (XRD) analysis revealed that the synthesized materials possess a high degree of crystallinity. The linearized enhanced plane wave full potential (FP- LAPW) approach based on the density functional theory (DFT) has been used to theoretically examine structural, the electronic, and optical properties of the CH3NH3PbX3(X=I and Br) thin film. The MAPbI3 thin film crystallizes in a tetragonal structure, while both MAPbBr3 perovskite thin film choose a cubic structure with different lattice parameters. The films exhibit homogeneity and a well-ordered crystalline structure, with distinct atomic planes visible in the analysis and high absorbance in the UV–Vis range, with bandgap energy around 1.50 and 2.20eV for CH3NH3PbX3(X=I and Br, respectively). The values we obtained are consistent with the theoretical predictions of the band gap energies as 2.04 eV for MAPBr3 and 1.14 eV for MAPI3. Moreover, both MAPI3 and MAPBr3 thin films demonstrate significant absorption in the visible region, around 80 %. This work is a detailed characterization of MAPbX3 lab-synthesized materials to pave the way toward their commercialization as precursors for perovskite based optoelectronic devices.

Morphological, structural, electronic and optical properties of deposited 4d-Mo doped TiO2 thin films compared to first-principles calculations

The present work reports the theoretical and experimental studies of structural, the electronic and optical properties of the TiO2 and Mo-doped TiO2 thin film. The linearized enhanced plane wave full potential (FP-LAPW) approach based on the density functional theory (DFT) has been used to theoretically examine structural, the electronic, and optical properties of molybdenum-doped TiO2 for various Mo concentrations (2 %, 4 %, 6 %). The band gap value is enhanced substantially, so it remains comparable to the experimental value of 3.00 eV and the Fermi level of MTO shifts downward in the valence band. This shift is originated mainly from the Mo-3p states, with a minor contribution by the Ti-3d and O-2p states. Undoped and Mo-doped TiO2 films were synthesized using the sol-gel spin coating technique as an experimental approach. The spectra obtained through X-ray Diffraction (XRD) indicated the presence of both anatase and rutile phases with no additional secondary phases detected. Scanning electron microscopy (SEM) analysis indicated that the thin films consisted of spherical, homogeneous nanoparticles that decreased in size as the Mo doping level increased. In addition, the transmittance spectrum showed a dip near 380 nm, consistent with the optical band gap, showing that the TiO2 films are absorbing in both the UV and visible domains. The band gap of the Mo doped TiO2 was reduced from ∼3.38 eV to ∼3.19 eV with an increase in Mo doping percentage.

Exploring the structural, electronic, optical, and thermoelectric properties of potassium-based double perovskites K2AgXI6 (X = Sb, Bi) compounds: A DFT study

Currently, lots of studies are going to find out the quality of the materials that could be used in solar cells and energy storage devices because of their higher absorption and utmost conductivity. We used density functional theory simulations utilizing the full potential linear augmented plane-wave approach. The generalized gradient approximation functional intended for materials (PBE-GGA) was utilized to compute structural characteristics, although the modified Becke and Johnson (mBJ) potential functional was employed to compute optoelectronic and thermalproperties. Their band gaps, may capture electromagnetic waves in the IR to the visible spectrum, rendering them appealingfor optoelectronics devices. Achieving the highest values of transition in the visible region against photon energy in the optical characteristics suggested that investigated double perovskites could be used in solar cells. Additionally, the transport characteristics premeditated using the Boltzmann transport equation indicate that the temperature and chemical potential in K2AgSbI6 to K2AgBiI6 perovskites might be used to make them suitable for solar energy. In order to investigate the optoelectronic as well as thermoelectric characteristics of K2AgXI6 (X = Sb, Bi)compounds used in energy storage devices.

Fast Orbital-Free Full-Potential Calculations for Large Nano Objects: C, Al and Ti

In the context of a full-potential orbital-free approach for the modeling of multi-atomic systems we investigated the dependence of the cohesive energies and bulk elastic modules of the large nanosystems Cn (n is up to 4096 atoms), Aln (n is up to 23,328 atoms) and tin (n is up to 2160 atoms). It was shown that the cohesive energies and elastic modules tend towards bulk crystal values at n ≈ 3000 for Cn systems, at n ≈ 1500 for Tin and at n ≈ 20,000 for Aln. The execution time for one energy iteration for Ti23328 was only 23 min.

Variational projector-augmented wave method: A full-potential approach for electronic structure calculations in solid-state physics

In solid-state physics, energies of crystals are usually computed with a plane-wave discretization of Kohn-Sham equations. However the presence of Coulomb singularities requires the use of large plane-wave cut-offs to produce accurate numerical results. In this paper, an analysis of the plane-wave convergence of the eigenvalues of periodic linear Hamiltonians with Coulomb potentials using the variational projector-augmented wave (VPAW) method is presented. In the VPAW method, an invertible transformation is applied to the original eigenvalue problem, acting locally in balls centered at the singularities. In this setting, a generalized eigenvalue problem needs to be solved using plane-waves. We show that cusps of the eigenfunctions of the VPAW eigenvalue problem at the positions of the nuclei are significantly reduced. These eigenfunctions have however a higher-order derivative discontinuity at the spheres centered at the nuclei. By balancing both sources of error, we show that the VPAW method can drastically improve the plane-wave convergence of the eigenvalues with a minor additional computational cost. Numerical tests are provided confirming the efficiency of the method to treat Coulomb singularities.

Magnetically Activated Electroactive Microenvironments for Skeletal Muscle Tissue Regeneration

This work reports on magnetoelectric biomaterials suitable for effective proliferation and differentiation of myoblast in a biomimetic microenvironment providing the electromechanical stimuli associated with this tissue in the human body. Magnetoelectric films are obtained by solvent casting through the combination of a piezoelectric polymer, poly(vinylidene fluoride-trifluoro-ethylene), and magnetostrictive particles (CoFe2O4). The nonpoled and poled (with negative and positive surface charge) magnetoelectric composites are used to investigate their influence on C2C12 myoblast adhesion, proliferation, and differentiation. It is demonstrated that the proliferation and differentiation of the cells are enhanced by the application of mechanical and/or electrical stimulation, with higher values of maturation index under mechanoelectrical stimuli. These results show that magnetoelectric cell stimulation is a full potential approach for skeletal muscle tissue engineering applications.

Electronic band profiles and optical response of Cd3Y2 (Y= N, P and As) compounds

Cubic and tetragonal phases of Cd3Y2 (Y= N, P and As) compounds are studied using full potential approach of density functional theory. All the studied crystal structures were fully optimized using the generalized gradient approximation. Calculated structural parameters agree well with experimental measurements. Electronic band profiles reveal metallic nature of Cd3Y2 in both phases except Cd3P2 which is semiconductor with small band gap value. The charge sharing is dominant in cubic and tetragonal phases which show covalent bond nature. Optical properties of the compounds are studied in detail in both phases. Interestingly, it is revealed that the intraband transitions play vital rule in explaining the optical properties in the metals while no influence observed in the Dirac semi-metal and semiconducting nature in these compounds. The reflectivity of metallic behavior compounds Cd3P2 and Cd3As2 reached up to 90% with the intra band calculation.

Combining electronic structure and many-body theory with large databases: A method for predicting the nature of 4f states in Ce compounds

Here we present the first large scale investigation of electronic properties and correlated magnetism in Ce-based compounds accompanied by a systematic study of the electronic structure and 4f-hybridization function of a large body of Ce compounds. We systematically study the electronic structure and 4f-hybridization function of a large body of Ce compounds with the goal of elucidating the nature of the 4f states and their interrelation with the measured Kondo energy in these compounds. The hybridization function has been analyzed for more than 350 data sets of cubic Ce compounds using electronic structure theory that relies on a full-potential approach. We demonstrate that the strength of the hybridization function, evaluated in this way, allows us to draw precise conclusions about the degree of localization of the 4f states in these compounds. The theoretical results are entirely consistent with all experimental information, relevant to the degree of 4f localization for all investigated materials. Furthermore, a more detailed analysis of the electronic structure and the hybridization function allows us to make precise statements about Kondo correlations in these systems. The calculated hybridization functions, together with the corresponding density of states, reproduce the expected exponential behavior of the observed Kondo temperatures and prove a consistent trend in real materials. This trend allows us to predict which systems may be correctly identified as Kondo systems. A strong anti-correlation between the size of the hybridization function and the volume of the systems has been observed. Our approach demonstrates the predictive power of materials informatics when a large number of materials is used to establish significant trends which can be used to design new materials with desired properties.

Sublattice dependent magnetic response of dual Cr doped graphene monolayer: a full potential approach

In the present scenario, many researchers are exploring the possibility of inducing a magnetic channel in graphene by introducing various types of defects. To examine the Cr–Cr interactions in dual Cr doped graphene monolayer for magnetic response and spin polarization, the first-principles density functional theory based calculations are performed. Further, the possibility of achieving 100 % spin polarization in various possible configurations of dual Cr-doping have been explored. Dual doping of Cr atoms in graphene monolayer preferring ferromagnetic ordering, generates a spin magnetic state with a local moment of ~4.00 µB. Depending upon the relative position of two Cr impurities in graphene, the ground states of doped systems are found be ferromagnetic, antiferromagnetic or paramagnetic. The origin of particular magnetic state observed in all possible dual Cr-doping configurations has been explained on the basis of RKKY indirect exchange interactions.

A full-potential approach to the relativistic single-site Green’s function

One major purpose of studying the single-site scattering problem is to obtain the scattering matrices and differential equation solutions indispensable to multiple scattering theory (MST) calculations. On the other hand, the single-site scattering itself is also appealing because it reveals the physical environment experienced by electrons around the scattering center. In this paper we demonstrate a new formalism to calculate the relativistic full-potential single-site Green’s function. We implement this method to calculate the single-site density of states and electron charge densities. The code is rigorously tested and with the help of Krein’s theorem, the relativistic effects and full potential effects in group V elements and noble metals are thoroughly investigated.

Local environment of metal ions in phthalocyanines: K-edge X-ray absorption spectra.

We report a detailed study of the K-edge X-ray absorption spectra of four transition metal phthalocyanines (MPc, M = Fe, Co, Cu and Zn). We identify the important single and multiple scattering contributions to the spectra in the extended energy range and provide a robust treatment of thermal damping; thus, a generally applicable model for the interpretation of X-ray absorption fine structure spectra is proposed. Consistent variations of bond lengths and Debye Waller factors are found as a function of atomic number of the metal ion, indicating a variation of the metal-ligand bond strength which correlates with the spatial arrangement and occupation of molecular orbitals. We also provide an interpretation of the near edge spectral features in the framework of a full potential real space multiple scattering approach and provide a connection to the local electronic structure.

Density-functional theory of the magnetic anisotropy of nanostructures: an assessment ofdifferent approximations

We discuss the multiple technical choices that have to be made in ab initio density-functionalcalculations of the magnetic anisotropy of supported nanostructures: (i) choice of theexchange–correlation functional, (ii) degree of optimization of the geometry of theadsorbate/substrate complex, (iii) magnetic anisotropy energy calculated self-consistently orvia the ‘force theorem’, (iv) calculations based on slab models of the substrate or using aGreen’s function describing a semi-infinite substrate, (v) full potential approach oratomic-sphere approximation. Using isolated Fe and Co atoms on Pt(111) as an examplewe demonstrate that by using a judicious combination of relatively crude approximations(complete neglect of structural relaxation, local exchange–correlation functional,...) seemingly good agreement with experimental anisotropy energies can beachieved, while the calculated orbital moments remain small. At a higher levelof theory (relaxed adsorbate/substrate complex, gradient-corrected functionals,...) providing a realistic geometry of the adsorbate/substrate complex and hence a correctdescription of the interaction between the magnetic adatom and its ligands, anisotropyenergies are also in semi-quantitative agreement with experiment, while the orbitalmoments of the adatoms are much too small. We suggest that the anisotropy energiesprovided by both approaches should be considered as lower limits of the real anisotropies.Without relaxation the ligand effect coupling the orbital moments of the adatom to theheavy atoms of the substrate is underestimated, while in a relaxed adsorbate/substratecomplex the lack of orbital dependence of the exchange potential combined with a stronghybridization of adatom and substrate states leads to a strong underestimation of theorbital moment. We have briefly explored the influence of post-density-functionalcorrections. Adding a modest on-site Coulomb repulsion to the d states of the adatom (in aDFT+U approach) leads to a modest increase of spin and orbital moments of the adatomaccompanied by a slow decrease of the induced moments, leaving the anisotropy energyalmost unchanged.

Effect of metal vacancies on the energy parameters of s-, p-, and d-metal diborides

For a group of s-, p-, and d-metal diborides (MB2, where M = Mg, Al, Sc, Ti, V, Y, Zr, Nb, or Ta), variations in the cohesive energy and the formation energy in the presence of cation vacancies (MB2 → M0.75B2), as well as the formation energy of cation-site vacancies, are analyzed using the FLMTO-GGA full-potential approach. The cationic nonstoichiometry for MB2 phases is achievable only when they are prepared under nonequilibrium conditions.

Electronic structure, stability and bonding of the Li-N-H hydrogen storage system

The Li-N-H system holds great promise for on-board hydrogen storage applications, particularly due to reversible interactions among lithium amide $(\mathrm{Li}\mathrm{N}{\mathrm{H}}_{2})$, imide $({\mathrm{Li}}_{2}\mathrm{N}\mathrm{H})$, and hydride (LiH). However, practical applications of the system are hindered by the relatively high stabilities of the compounds and uncertainty of their reaction paths. Understanding the mechanism of hydrogen interactions with the host structures is essential for further development. Here, we calculated the electronic structures and total energies of lithium hydride (LiH), lithium imide $({\mathrm{Li}}_{2}\mathrm{N}\mathrm{H})$, and lithium amide $(\mathrm{Li}\mathrm{N}{\mathrm{H}}_{2})$ using a first-principles full potential approach. The estimated formation enthalpies for the two-step reactions, ${\mathrm{Li}}_{3}\mathrm{N}+2{\mathrm{H}}_{2}\ensuremath{\leftrightarrow}{\mathrm{Li}}_{2}\mathrm{N}\mathrm{H}+\mathrm{Li}\mathrm{H}+{\mathrm{H}}_{2}\ensuremath{\leftrightarrow}\mathrm{Li}\mathrm{N}{\mathrm{H}}_{2}+2\mathrm{Li}\mathrm{H}$ are $\ensuremath{-}162.05$ and $\ensuremath{-}40.94\phantom{\rule{0.3em}{0ex}}\mathrm{kJ}∕\mathrm{mol}$, comparable to the experimental values of $\ensuremath{-}165$ and $\ensuremath{-}45.5\phantom{\rule{0.3em}{0ex}}\mathrm{kJ}∕\mathrm{mol}$, respectively. The bonding interaction characteristics and the stability of these materials were further analyzed from the electronic structures. It is noted that the N atom bonds unequally with the two H atoms in lithium amide. As a result, the amide $\mathrm{Li}\mathrm{N}{\mathrm{H}}_{2}$ can dissociate in two almost equivalent transient steps: ${\mathrm{Li}}^{+}+{(\mathrm{N}{\mathrm{H}}_{2})}^{\ensuremath{-}}$; and ${(\mathrm{Li}\mathrm{N}\mathrm{H})}^{\ensuremath{-}}+{\mathrm{H}}^{+}$. The reaction of the relevant species may evolve $\mathrm{N}{\mathrm{H}}_{3}$ as a transient gas in the $(\mathrm{Li}\mathrm{N}{\mathrm{H}}_{2}+\mathrm{Li}\mathrm{H})$ system.

High‐pressure phase transitions in semimagnetic semiconductor I: Pb1–xMnxS

AbstractPressure‐induced structural phase transitions in Pb1–xMnxS (0 < x < 0.05), from the rocksalt (B1) to the CsCl (B2) type phase, have been calculated. The present study of the phase transition is based on the three‐body potential (TBP) approach, which includes long‐range as well as short‐range interactions. The long‐range part consists of a Coulomb and three‐body interactions, whereas the short‐range part includes the van der Waals and overlap repulsive interactions. In order to strengthen the significance of our results and verify the presence of intermediate orthorhombic phase during B1 to B2 structural transition in the host binary compound PbS we performed first principles full potential linear muffin tin orbital approach and provided a good support to our TBP results. Our first‐principles calculations, based on the full potential muffin tin orbital (FPLMTO) method, successfully predicts the TlI type phase and supports the TBP results.

Solution of periodic Poisson's equation and the Hartree–Fock approach for solids with extended electron states: Application to linear augmented plane wave method

AbstractWe formulate a Hartree–Fock‐LAPW method for electronic band structure calculations. The method is based on the Hartree–Fock–Roothaan approach for solids with extended electron states and closed core shells where the basis functions of itinerant electrons are linear augmented plane waves. All interactions within the restricted Hartree–Fock approach are analyzed and in principle can be taken into account. In particular, we obtained the matrix elements for the exchange interactions of extended states and the crystal electric field effects. To calculate the matrix elements of exchange for extended states, we first introduce an auxiliary potential and then integrate it with an effective charge density corresponding to the electron exchange transition under consideration. The problem of finding the auxiliary potential is solved by using the strategy of the full potential LAPW approach, which is based on the general solution of periodic Poisson's equation. Here, we use an original technique for the general solution of periodic Poisson's equation and multipole expansions of electron densities. We apply the technique to obtain periodic potentials of the face‐centered cubic lattice and discuss its accuracy and convergence in comparison with other methods. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Why the all-electron full-potential approach is suitable for calculations on fullerenes and nanotubes?

Already 30 years have passed since the first prediction of C 60 by Professor Osawa. A family of cage-type fullerenes and carbon nanotubes were experimentally found as the third form of carbon molecules in the 1980s. After this discovery, much research has been conducted experimentally and theoretically on these new materials. The all-electron full-potential approach is important for fully understanding the quantum mechanical behavior of the fullerenes and related molecules. We show some results of band calculations and ab initio molecular dynamics.

Electronic theory of phase stability in substitutional alloys: application to the Au–Ni system

Abstract The total energies of formation of Au–Ni superstructures based on a fcc lattice have been calculated using the linear muffin-tin-orbital (LMTO) method in the full potential approach. Both unrelaxed and relaxed structures have been included in the calculations. The energy of formation is decomposed into three terms, a volume deformation contribution, a chemical contribution and a relaxation contribution. The enthalpy of mixing of the disordered solid solution has been calculated using an Ising-like cluster expansion for both the chemical and relaxation effects. In the Gibbs energy of mixing, a configurational entropy of mixing has been calculated with the cluster variation method (CVM) and the thermal excitations due to electronic and vibrational effects have been taken into account. The miscibility gap displayed in the Au–Ni system has been calculated. The results are discussed in comparison with the experimental data.

Theoretical LEED parameters for the zinc-blende GaN (110) surface

We present a theoretical study of the equilibrium atomic structure of the GaN (110) surface based on accurate, parameter-free, self-consistent total energy and force calculations using the density functional theory, the local-density approximation for the exchange–correlation term and the full potential linear augmented plane wave approach associated to the slab supercell model. We are concerned with the LEED parameters Δ 1⊥, Δ 1 x , Δ 2⊥, d 12⊥, d 12 x and ω for the (110) surface. We analyze the changes in the bond-lengths and in the bond-angles at the anion and cation sites. We conclude that similarly to the III-Arsenides (110) and III-Phosphides (110) surfaces the GaN (110) surface relax such that the Ga-surface atom moves inward and the N-surface atom moves outward. The driving mechanism for this atomic rearrangement is that the Ga atom tends to a planar sp 2-like bonding situation with its three N neighbours and the N atom tends to a p-bonding with its three Ga neighbors.

Phase-stability study of the Al-Nb system

The total energies of formation of Al-Nb intermetallic phases ${\mathrm{Nb}}_{3}\mathrm{Al}$ $(A15),$ ${\mathrm{Nb}}_{2}\mathrm{Al}$ (\ensuremath{\sigma}), and ${\mathrm{NbAl}}_{3}$ ${(DO}_{22})$ have been calculated using the linear-muffin-tin-orbital (LMTO) method in the full potential (FP) approach. Relaxation and distortion effects have been included and have been shown to play an important role in the stabilization of the ${\mathrm{DO}}_{22}$ intermetallic phase. In order to get the interaction parameters to describe the energetics of the bcc and fcc solid solutions, FP-LMTO calculations have been performed for various superstructures based on the bcc and fcc lattices. To discuss thermodynamic properties and the phase diagram of the Al-Nb system, the cluster variation method configurational entropy has been introduced using the tetrahedron-octahedron approximation in the fcc solid solution and the tetrahedron approximation in the bcc solid solution. The thermodynamic data obtained in this work agree fairly well with the available experimental data. Connections with Calphad approaches are also discussed. An attempt to calculate composition-temperature phase diagram of the Al-Nb system is presented, using a semiempirical treatment of the liquid phase.