DV-Xα Method Research Articles

Theoretical Analysis of Anomalous Emission of Eu2+ in Crystals By First-Principles Calculation

The 5d-4f transition energies of lanthanides are very versatile, especially the 4f65d1-4f75d0 transition energy of Eu2+ has high luminescence efficiency and is used in various luminescent materials such as phosphors like SrxCa1-xAlSiN3: Eu2+, scintillators, and solid-state lasers, etc. However, there are materials that do not undergo pure 5d-4f transitions, showing the so-called anomalous luminescence instead. The anomalous luminescence is caused by the formation of excitons due to the overlap of the 5d level of Eu2+ with the conduction band and the transition of electrons from the conduction band to the 4f level, resulting in a shift to a lower energy than the general 5d-4f transition energy. A more detailed analysis of this phenomenon is important for the development of novel luminescent materials using Eu2+.In this study, we aimed to theoretically analyze the anomalous luminescence based on first-principles electronic structure calculations. The model clusters of Eu2+-doped crystals consisting of Eu2+ at the substitution site and the surrounding ions were created. Then molecular orbital calculations were performed by the relativistic discrete-variational Xα (DV-Xα) method and subsequently multiplet calculations were performed by the relativistic discrete-variational multi-electron (DVME) method. These first-principles calculations were carried out for Eu2+-doped crystals that show anomalous luminescence and those that do not show anomalous luminescence, and the electronic states of these materials were compared in detail.

Prediction of 4f-5d Transition Energy of Ce3+ in Oxides By First-Principles Calculations and Machine Learning

A Ce3+ ion has only one electron in the 4f orbitals and its 4f-5d transition energy is strongly influenced by the width of the crystal field splitting of the 5d orbitals. In other words, the absorption and emission wavelengths of Ce3+ in crystals can be widely controlled by changing the ligand field environment. As an example of Ce3+-doped phosphor, Ce:YAG (Y3Al5O12) is widely used as an yellow phosphor for standard white LEDs. Therefore, novel phosphors with desired emission colors can be developed by adding Ce3+ to appropriate host crystals.In this work, we aimed to construct an efficient prediction model for the transition energy of Ce3+ in oxide crystals. Small clusters consisting of the substituted Ce3+ ion and the first-neighbor anions were constructed and molecular orbital calculations were performed using the relativistic discrete-variational Xα (DV-Xα) method. Then machine learning based on structural and electronic state parameters was performed to create a predictive model for the 4f-5d transition energy of Ce3+ in crystals. By creating the correlation diagrams, the influence of each parameter on the transition energy was analyzed in detail.

Systematic First-Principles Calculations of Ce3+-Dopant in Garnet-Type Oxide Phosphors

A study of Ce3+-doped oxide phosphors was performed using first-principles calculations based on the relativistic DV-Xα method. In particular, we focused on the Ce3+-doped garnet-type oxides, which have potential applications in solid-state lighting and display devices. The electronic structure and optical properties of the phosphors were analyzed. The energy levels of the Ce3+ ions were affected by the coordination number and the crystal field strength of the surrounding oxygen ions. In addition, the crystal structure of the material had a significant impact on the energy levels of the Ce3+ ions, with different crystal structures leading to different energy levels.The Ce3+ ion is substitutionally incorporated in the garnet lattice, and the 4f electron of Ce3+ plays an important role in the luminescence of the material. The emission wavelengths of the 5d-4f transition energy of Ce3+ can be tailored by varying the crystal structure and the composition. The 5d orbitals of Ce3+ are substantially affected by the crystal field splitting while the amplitude of crystal field splitting (εcfs) is caused by many parameters: coordination number, symmetry of Ce3+ site, and bond lengths between the Ce3+ ion and the oxygen ions (O2-). This study incorporated the following computational conditions: i) lattice relaxation, ii) the choice of the exchange-correlation potential, and iii) Slater’s transition state method. The effects of these conditions were analyzed. In addition, the correlations among physical properties and electronic structure parameters were also investigated in detail.The first-principles calculation results were compared to the experimental data to validate the accuracy of the theoretical models, which showed a good agreement between the experimental and predicted values.

Electronic Structure Calculation of Cr3+ and Fe3+ in Phosphor Host Materials Based on Relaxed Structures by Molecular Dynamics Simulation

The electronic structures of the luminescent center ions Cr3+ and Fe3+ in the deep red phosphors LiAl5O8:Cr3+, α-Al2O3:Cr3+, and γ-LiAlO2:Fe3+ were calculated by the DV-Xα method, in which the local distortion induced by the replacement of Al3+ sites in the host crystals by the luminescent center ions was reproduced by classical molecular dynamics (MD) simulation. The MD simulations based on classical dynamics allowed for the handling of more than 1000 atoms for the lattice relaxation calculations, which was advantageous to simulate situations in which a small number of foreign atoms (ions) were dispersed in the host lattice as in phosphors, even when typical periodic boundary conditions were applied. The relaxed lattices obtained after MD indicated that the coordination polyhedra around Cr3+ and Fe3+ expanded in accordance with the size difference between the luminescent center ions and Al3+ in the host crystals. The overall profiles of the partial density of states (p-DOSs) of the isolated Cr3+ and Fe3+ 3d orbitals were not significantly affected by the lattice relaxation, whereas the widths of the energy splitting of the 3d orbitals were reduced. The electronic structure calculations for Fe–Fe pairs in γ-LiAlO2 showed that the antiferromagnetic interactions with antiparallel electron spins between the Fe3+ ions were preferred, especially when the Fe–Fe pair was on the first-nearest neighboring cation sites.

Chromaticity coordinates of ruby based on first-principles calculation

Understanding the local atomic configuration is crucial for studying phosphor materials. Their performance in many applications is strongly dependent upon their optical properties. Much experimental and theoretical effort has been made to meet the requirements. Specifically, ab-initio studies have extensively reported the absorption spectra and the multiplet energies of phosphors. However, the qualitative analysis on the emitted light has not yet been reported. In this work, we characterized the emitted light of ruby, which is a widely studied phosphor material. The absorption spectra of ruby were calculated utilizing the non-empirical discrete variational Xα (DV-Xα) and discrete variational multi-electron (DVME) software. Then, the investigation on the ( x , y ) chromaticity coordinates of was performed under the standard illuminant D65 utilizing ColorAC software, a chromaticity diagram maker. In this work, we used a ruby model cluster generated from an α-Al 2 O 3 crystal. The model consists of seven atoms, where one chromium atom surrounded by six oxygen atoms. We compared the absorption spectra obtained via simple configuration interaction (CI) and those obtained which include energy corrections called configuration dependent correction (CDC) and correlation correction (CC). We successfully reproduced the color that is observed in experiment. The chromaticity coordinates approach red region for higher concentration. The results show that the calculation with CDC-CC shows better agreement with experiment. This research confirms the non-empirical calculations based on the DV-Xα and DVME methods, in the terms of emitted light. • The emitted light of α-Al2O3: Cr3+ (ruby) was characterized non-empirically. • Effects of CDC-CC correction were investigated thoroughly. • The “theoretical color” reproduced the tendency of the “experimental color”. • The calculation with CDC-CC correction shows better agreement.

An analysis of luminous mechanism of rare earth hybrid complex with Ce3+ ion by the DV-Xα method

In recent years, rare earth compounds with Ce3+ ion have reported as light-emitting materials due to photoluminescence. But Ce3+ ion luminous mechanism has not yet particularly reported until now on account of disparate ligands. In this report, results of study manifested it would possible make complicated, which coordinated by ligands upon π conjugation. In this study, several fluorescent compounds as well as non-fluorescent compounds have synthesized by solution method, which coordinated by common organic ligands with π conjugation, such as acetylacetonato(acac), oxalate(ox), 2,2′-bipyridine(bpy), 1,10-phenanthroline(phen). It have been made clear about Luminous mechanism by means of experimentation compare to molecular orbital method.

Development of Austenite Fe Alloy for Melted Zinc Coating Facilities Using the DV-Xα Methods

Development of Austenite Fe Alloy for Melted Zinc Coating Facilities Using the DV-Xα Methods

First-Principles Study of the Crystal-Field and Racah Parameters of Cr3+ in Alumina

The development of blue LEDs [1] enabled one to construct white LEDs by combining them with appropriate phosphors. Recently Mn4+-doped fluorides have been put into commercial use as the red phosphors for high color-rendering white LEDs [2]. However, in order to suppress the degradation due to high humidity and high temperature, a special surface treatment is required for these phosphors. Therefore, the search of other red phosphors activated by Mn4+ is still desired. For theoretical design of novel phosphors, non-empirical prediction of optical parameters such as the crystal-field and Racah parameters is quite important. The purpose of this study is to establish a first-principles approach to predict these parameters of transition metal ions in crystals.In this work, the crystal-field and Racah parameters of ruby (Cr3+ doped α-Al2O3) were evaluated based on the first-principles calculations using the relationship between the ligand-field theory and the molecular orbital (MO) theory derived by Sambe and Felton [3]. Two types of first-principles methods were adopted. One is the discrete-variational (DV)-Xα method [4], which is an MO calculation method based on the one-electron approximation. The other is the discrete variational multi-electron (DVME) method [5], which is a configuration-interaction (CI) calculation method based on the explicit many-electron wave functions. The estimation of the crystal-field and Racah parameters were performed in the following three approaches.(1) Estimation based only on the DV-Xα method(2) Estimation based only on the DVME method(3) Estimation based on the combination of the DVME method and the DV-Xα methodThe results show that the values of the crystal-field and Racah parameters obtained by the approach (3) are in the best agreement with the values obtained by fitting to the experimental data [6], indicating that CI calculations using some corrections based on the one-electron MO calculations are effective for the non-empirical estimation of the crystal-field and Racah parameters [7]. These results also provide theoretical basis for the configuration-dependent correction and the correlation correction introduced in our previous CI calculations of ruby [5]. This approach could be applied to prediction of d-d transitions of Mn4+ in crystals to find a suitable host for novel Mn4+-activated red phosphors for white LEDs.[1] I. Akasaki and H. Amano, Jpn. J. Appl. Phys. 45, 9001 (2006).[2] J. E. Murphy, F. Garcia-Santamaria, A. A. Setlur, and S. Sista, SID 2015 DIGEST, 927 (2015).[3] H. Sambe and R. Felton, Int. J. Quant. Chem., 10, 155 (1976).[4] H. Adachi, M. Tsukada, and C. Satoko, J. Phys. Soc. Jpn. 45, 875 (1978).[5] K. Ogasawara T. Ishii, I. Tanaka, and H. Adachi, Phys. Rev. B 61, 143 (2000).[6] W. M. Fairbank, Jr., G. K. Klauminzer, and A. L. Schawlow, Phys. Rev. B 11, 60 (1975).[7] K. Ogasawara, K.C. Mishra, and J. Collins, ECS J. Solid State Sci. Technol. 9, 016011 (2020).

Preface

It is an honour for Universitas PGRI Semarang (UPGRIS-Indonesia) to be the host of the 7th International Conference on DV-Xα Method: The Advances-Related Experiments andTheories on Material Science (ICDM 2019). We are pleased to have cooperation with DVXα Society to hold this international event. As we know, the previous conferences related to this topic had been conducted six times: once in Hungary, three times in South Korea, two times in Japan and supported by some institutions as the hosts: The Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI-Hungary), Seoul National University (South Korea), Kunsan National University (South Korea), National Institute of Physical and Chemical Research (RIKEN-Japan), Korean Basic Science Institute (KBSISouth Korea), and University of Hyogo (Japan).ICDM 2019 was an international event aimed at presenting contemporary research and accommodating discussion for scientists, scholars, engineers, students, research institutes, and industries in the field of advanced materials, science and information technology. It was successfully held on 2 - 4 September 2019 in Semarang, Indonesia. This event was organized by Universitas PGRI Semarang (UPGRIS - Indonesia) in cooperation with DVXa Society (Japan), Kwansei Gakuin University (Japan), Kobe University (Japan), Universitas 17 Agustus 1945 Semarang (Indonesia), Universitas PGRI Madiun (Indonesia) and under the coordination of Centre of Science and Technology UPGRIS (Indonesia).ICDM 2019 was attended by 110 participants, and a total of 60 papers were presented and discussed. The papers were authored by 30 students and 34 lecturers. Categories of presentation sessions were divided into two sessions; lecture and poster sessions. There were 4 keynote speakers, 18 invited speakers, 20 general speakers who delivered the talks in lecture sessions and 18 poster presenters. Conference presenters were from various countries, 1 presenter from the United States, 1 presenter from Thailand, 1 presenter from South Korea, 1 presenter from Estonia, 25 presenters from Japan, 1 presenter from Ukraine and 30 presenters from Indonesia.We are proud and grateful for the interest you expressed in the discussion of this theme. It provoked discussion among participants over the best ways to implement DV-Xα Method in advances experiments on material sciences. Throughout the process, hopefully we could contribute answers or alternative solutions for the demand of the progressing industry in regards to advanced materials to support the development of many countries.

Mechanism of Optical Rotation of Amino Acids Using Electronic State Calculation

Because of the chiral nature of the building blocks of living matter, an optical phenomena associated with the chirality constitute an important topic in physical chemistry. The specific optical rotation, which is a parameter for the characterization of the natural optical activity, depends strongly on the conformation of the molecule. In this study, we investigated the dependence of the optical rotation on a molecular conformation in the gas phase by calculating the electronic states of seven kind of chiral amino acids using the DV-Xα method. As a result, we can confirm the existence of an antibonding orbital on the side chain and the optical rotations are strongly related.

Effects of Transition Metal Doping to Cerium-Oxides in Thermal Reduction Reaction

Considering our lives, novel energy production is so required, and many scientists have been investigated this problem from a lot of views. One of the ways for the new energy productions is the solar power thermochemical production by an oxidation-reduction reaction of the ceramics CeO2 (ceria). In this research, the ceria is used for obtaining an H2 gas in vapor reaction in high-temperature thermal equipment which has a heat production system consisting by focused sun light. Nowadays technology has been also developed to keep a human living, not to harm the Earth environment. From these points, it is realized that how important the H2 gas is for our lives, so we are trying to improve the thermochemical H2 gas production by means of a ceria as a catalyst. Our purpose in this study is, to point out what effects occur in doped ceria’s thermal reduction (TR) reaction by using DV-Xα method. Comparing the models between the pure ceria and the Mn doped ceria, we have realized the difference by the reaction. In this appearance, one of the considerations is a view from p-DOSs (partial-Density of States), in which there are different O-2p DOSs by different crystal structures. From this view, we considered that the ceria structure would become more stable to keep the stable cyclic thermal reaction in Mn doped ceria.

The magnetism change by Jahn-Teller distortionin octahedral hexa-coordinate complex

Metal complexes exhibit significant physical properties such as electrical conductivity, magnetism and optical properties. They can be controlled by changing the ligand field splitting of the d-orbital of the central metal ion. We have investigated the reversible spin crossover (SCO) phenomenon by changing the ligand field splitting in six-coordinated metal complexes ML6. In this study, we focused on the change of the spin states by uniaxial Jahn-Teller distortion in the case of an octahedral hexa-coordinated metal complexes ML6, involving two types of different ligand molecules. In addition, we have used DV-Xα and DVME methods in order to calculate the electronic states. In order to reproduce the effect of the Jahn-Teller distortion in the calculation, a uniaxial anisotropic distortion has been applied into the octahedral hexa-coordinate metal complex. The purpose of this research is to study the mechanism and phenomenon of the spin state changing by discussing the calculated electronic states of the spin crossover phenomenon.

Optical properties of Co3+ doped in α-Al2O3 with Considering Lattice Relaxation Effect

Search of new luminescence materials to improve the current white-ight emitting diode (LED) is still ongoing. Several investigations such as the ion dependence, the host crystal dependence has been done previously. Since we want to get a complete picture of ion-host combination dependence, we investigated α-Al2O3: TM3+. In this work we estimated the optical properties of α-Al2O3 doped with Co3+. We constructed model clusters consisting of 7 atoms. The lattice relaxation effects due to the Co3+ substitution were calculated using Shannon’s crystal radii method and geometry optimizations in the Cambridge Serial Total Energy Package (CASTEP) method. The one-electron Discrete Variational-Xα (DV-Xα) method was used to estimate the molecular orbital energies, while the many-electron Discrete Variational Multielectron (DVME) method was used to estimate the d-d absorption spectra. Since Co3+ belongs to 3d 6 configuration, there are two possible spin states i.e., high-spin (HS) and low-spin (LS) states.

Lattice Relaxation Effects on the Multiplet Energies of Ruby Under Pressure using One-Electron Calculations

Up to recently, it has been difficult to calculate the multiplet energies of compounds using one-electron approach. Since it only considers one electron and one nuclei, the interaction among the electrons are neglected. Previously we have successfully estimated the 2E→ 4A2 (R-line) levels of ruby at 0 pressure using one-electron approach based on one-electron calculation using the first-principles Discrete Variational-Xα (DV-Xα) method. Here we want to perform similar investigation, not only for 0 pressure but up to 110 GPa. We estimated the lattice relaxation effect due to the Cr3+ substitution and due to the applied pressure by using two different methods i.e., Shannon’s crystal radii and geometry optimizations. Two different types of model cluster consisting of 7 and 63 atoms will be used. The 2E level is estimated by the barycenter of t2g 3 configuration which consists of 4 multiplets.

Single Crystal X-ray Structural Analysis and Electronic Theory of Sugar Molecules

Rare sugar is a monosaccharide that there are trace amounts in nature, natural sugars present in large amounts in nature world is referred to as a naturally monosaccharide. Recently, the isomerase called D-tagatose-3-epimerase (DTE) was discovered, and it has a possibility to synthesize quantity of the rare sugar from a natural sugar through the enzymatic reaction. And all of hexoses can be synthesized by four kinds of enzymatic reactions (oxidoreductase, aldose isomerase, aldose reductase and DTE reactions). In this study, single-crystal X-ray structure analysis of a sugar alcohol and its derivative have been performed in order to determine the absolute coordinates of these sugar molecules. We have also investigated the electronic state calculation by means of DV-Xα method using the obtained data of the absolute coordinates. We also consider that mechanism of the enzymatic reaction and intermolecular energy properly such as a hydrogen bond in order to synthesize the supramolecular rare sugars (SRSs) which can be controlled structures and the hydrogen bonds.

Recent applications of discrete variational multi-electron method

The discrete variational multi-electron (DVME) method is a first-principles many-electron calculation method based on the discrete-variational Xα (DV-Xα) molecular orbital method. There is also the relativistic version of the DVME method, which is based on the relativistic DV-Xα method. Since the explicit many-electron wave functions of the multiplet states of transition-metal (TM) or rare-earth (RE) ions in crystals can be obtained, the DVME method has been applied to the analyses of various luminescent materials such as solid-state lasers and phosphors. In this paper, as examples of the recent applications of the DVME method, the following researches will be briefly presented: (1) Visualization of the energy-structure relationship of Cr3+ in oxides, and (2) Creation of the predictive model of the multiplet energy using machine learning.

Effect of trivalent manganese substitution in α-Al2O3 crystal on the absorption spectra based on first-principles calculations

The absorption spectra of α-Al2O3: Mn3+ at low-spin (LS) state have been estimated based on first-principles calculations without referring to any experimental parameter. The effect of lattice relaxation due to the Mn3+ substitution was considered under several computational procedures such as the Shannon’s crystal radii method and the geometry optimization using Cambridge Serial Total Energy Package (CASTEP) code. Two different sizes of model clusters consisting of 7 and 63 atoms were compared. Next, the molecular orbitals (MO) were estimated using the one-electron calculations discrete variational-Xα (DV-Xα) method while the absorption spectra were estimated using the many-electron calculations discrete variational multi-electron (DVME) method. The results show that the lattice-relaxation ratio is about ca. 104.05-106.43% depending on the computational conditions. Due to the Mn-O bond-length elongation, the crystal field splitting (10Dq) decreased ca. 0.24-0.41 eV. Thus, the peak position originating from 3T1 → 3E transition energy shifted toward the lower energy ca. 0.10-0.26 eV. Both of the larger-cluster size and the lattice-relaxation effect decrease the peak energies.

A First-Principles Investigation of the Crystal-Field and Racah Parameters of Transition Metal Ions: Cr3+ in Alumina

The crystal-field and Racah parameters of ruby were evaluated based on the first-principles calculations using the relationship between the ligand-field theory and the molecular orbital theory derived by Sambe and Felton. It is found that the combination of the discrete variational (DV)-Xα calculations and the discrete variational multi-electron (DVME) calculations is effective for prediction of reasonable values for the crystal-field and Racah parameters for Cr3+ in alumina. These results indicate that the corrections to the DVME calculations based on the DV-Xα method provide a theoretical basis for the configuration-dependent correction and the correlation correction which were introduced in the previous calculation based on an intuition that the average transition energy should be reproduced better by one-electron calculations than many-electron calculations. This method could be used to predict the d-d transitions for Mn4+ to find a suitable host for a red phosphor for LED applications.

The determining factor of the luminescence energies of vanadate phosphors

The molecular orbital calculations based on the DV-Xα method were carried out for several vanadate phosphors of Sr2VO4Cl, Ca2VO4Cl, Ba2V2O7, Mg3(VO4)2, and Zn3(VO4)2, of which the luminescent colors range from deep-blue to yellow through green. The structural refinement with the X-ray diffraction technique preceded the DV-Xα calculations to provide a theoretical interpretation on the relationship between the crystal structures and the luminescent colors (luminescence energies) of the vanadate phosphors. The partial density of states obtained in the DV-Xα calculations reasonably explained the lowest excitation energies of the vanadate phosphors. The calculations also exhibited the difference in the bonding characters among the ligand oxygens in a VO4 tetrahedron due to the structural distortion. The relatively large contributions of the ionically coordinated oxygens were proposed on determining the luminescence energies. A linear correlation was deduced between the luminescence energies and the averaged V–O distances with the selected oxygens ionically coordinated to V.

Ab-initio study on the absorption spectrum of color change sapphire based on first-principles calculations with considering lattice relaxation-effect

In this study, we performed an investigation on α-Al2O3: V3+ material, or the so-called color change sapphire, based on first-principles calculations without referring to any experimental parameter. The molecular orbital (MO) structure was estimated by the one-electron MO calculations using the discrete variational-Xα (DV-Xα) method. Next, the absorption spectra were estimated by the many-electron calculations using the discrete variational multi-electron (DVME) method. The effect of lattice relaxation on the crystal structures was estimated based on the first-principles band structure calculations. We performed geometry optimizations on the pure α-Al2O3 and with the impurity V3+ ion using Cambridge Serial Total Energy Package (CASTEP) code. The effect of energy corrections such as configuration dependence correction and correlation correction was also investigated in detail. The results revealed that the structural change on the α-Al2O3: V3+ resulted from the geometry optimization improved the calculated absorption spectra. By a combination of both the lattice relaxation-effect and the energy correction-effect improve the agreement to the experiment fact.