Namsrai Tsogbadrakh | The National University of Mongolia (original) (raw)

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Papers by Namsrai Tsogbadrakh

arXiv (Cornell University), Feb 10, 2019

We have developed the Coulomb wave function discrete variable representation (CWDVR) method to so... more We have developed the Coulomb wave function discrete variable representation (CWDVR) method to solve the imaginary time dependent Kohn-Sham equation on the many-electronic second row atoms. The imaginary time dependent Kohn-Sham equation is numerically solved using the CWDVR method. We have presented that the results of calculation for second row Li, Be, B, C, N , O and F atoms are in good agreement with other best available values using the Mathematica 7.0 programm.

arXiv (Cornell University), Oct 2, 2018

We have been calculated the ground state charge densities and energies of noble gas atoms through... more We have been calculated the ground state charge densities and energies of noble gas atoms through a single time dependent quantum fluid Schrödinger equation. By using imaginary-time, the Schrödinger equation has been transformed into diffusion equation. This equation numerically solved through discrete variable representation (DVR) method. Instead of the usual finite difference method the radial coordinate is discretized using the discrete variable representation constructed from Coulomb wave functions. Our calculations were performed using the Mathematica 7.0 programm.

Journal of chemical physics online/The Journal of chemical physics/Journal of chemical physics, May 28, 2024

Mongolian journal of chemistry, Dec 27, 2019

In this study, the structure and electronic properties of the spinel compound Li 4 Ti 5 O 12 (LTO... more In this study, the structure and electronic properties of the spinel compound Li 4 Ti 5 O 12 (LTO) are investigated both theoretical and experimental methods. The experimental studies of structural and electronic properties were performed by X-ray diffraction and UV-visible spectroscopy. The first principles calculations allowed to establish the relationship between the structure and electronic properties. The spinel type structure of LTO is refined by the Rietveld analysis using the X-ray diffraction (XRD). The band gap of LTO was determined to be 3.55 eV using the UV-visible absorption spectra. The Density functional theory (DFT) augmented without and with the Hubbard U correction (GGA and GGA +U+J 0) is used to elucidate the electronic structure of LTO. We have performed systematic studies of the first principles calculations based on the GGA and GGA+U for the crystal structure and electronic properties of spinel LTO. We propose that a Hubbard U correction improves the DFT results.

Solid State Phenomena, 2018

Nanosized spinel Li4Ti5O12 was successfully synthesized by a solid state reaction method at 800°C... more Nanosized spinel Li4Ti5O12 was successfully synthesized by a solid state reaction method at 800°C according to the Li4Ti5O12cubic spinel phase structure. In this synthesizing process, anatase TiO2and Li2CO3were used as reactants. The average grain size of the synthesized powders was around 200 nm. The synthesized Li4Ti5O12powder was characterized X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectrometry (EDS), and Specific Surface Area Analyzer (BET, Brunner-Emmett-Teller) respectively. X-ray diffraction results show that calcination temperature and time have the important effects on the crystal structure of Li4Ti5O12powder. In this study, we used a first principle method, based on the density functional theory to explore electronic and structural properties of Li4Ti5O12, as anode material for lithium ion batteries. Differences on these properties between delithiation state Li4Ti5O12and lithiation state Li7Ti5O12are compared. All the predicted structural and electrochemical properties agree closely with the experimental findings in literature. The average intercalation voltage of 1.4V during charging/discharging were obtained. We have shown that the Li4Ti5O12material exhibits insulating behavior with the band gap of 3.16 and 3.90 eV using the GGA and GGA+U+J0calculations respectively. Li7Ti5O12becomes metallic as Li atoms inserted in Li4Ti5O12material. Spinel Li4Ti5O12has been regarded as an attractive anode material for the development of high-power lithium-ion batteries because of its unique attributes of high safety and rate capability.

Journal of Modern Physics, 2019

The self-consistent Kohn-Sham equations for many-electron atoms are solved using the Coulomb wave... more The self-consistent Kohn-Sham equations for many-electron atoms are solved using the Coulomb wave function Discrete Variable Method (CWDVR). Wigner type functional is used to incorporate correlation functional. The discrete variable method is used for the uniform and optimal spatial grid discretization and solution of the Kohn-Sham equation. The equation is numerically solved using the CWDVR method. First time we have reported the solution of the Kohn-Sham equation on the ground state problem for the many-electronic atoms by the CWDVR method. Our results suggest CWDVR approach shown to be an efficient and precise solution of ground-state energies of atoms. We illustrate that the calculated electronic energies for He, Li, Be, B, C, N and O atoms are in good agreement with other best available values.

$Research paper thumbnail of Удаан M^{-}+He мөргөлдөөний үед электроны корреляц тооцох асуудал$

background: Many NSTEACS patients are medically managed without coronary revascularization. The r... more background: Many NSTEACS patients are medically managed without coronary revascularization. The reasons vary and may impact prognosis. methods: EPICOR Asia (NCT01361386) is a prospective study of hospital survivors post ACS enrolled in 219 hospitals from 8 countries/ regions in Asia (06/2011-05/2012). All medically managed NSTEACS patients in EPICOR Asia were classified into 3 groups: 1) no coronary angiography (CAG-); 2) non-significant coronary artery disease (CAD) on angiogram (CAG+ CAD-); and 3) significant CAD (CAG+ CAD+). We compared baseline differences between groups, and report 1-y mortality rates. Results: Of 6,164 NSTEACS patients, 2,272 (37%) were medically managed only, with 1,339 (59%), 254 (11%) and 679 (30%) patients in the CAG-, CAG+ CAD-, and CAG+ CAD+ groups, respectively. There were marked differences in number of NSTEACS patients medically managed among the 8 countries/regions (13-81%). Between-group differences were seen in baseline characteristics (Table). CAG+ CADpatients were younger with fewer CV risk factors than CAG+ CAD+. CAG-patients were older, more likely with known CV disease, more frequently admitted to hospitals with no cath lab, and had the highest 1-y mortality (6.9% versus 3.3% for EPICOR Asia overall). conclusion: NSTEACS patients who are medically managed are a heterogeneous group with different clinical features and outcomes e.g. mortality risk. The factors underlying different management strategies, and to improve prognosis, need to be identified.

Proceedings of the Korean Magnestics Society Conference, Dec 1, 2011

A first-principles calculation implemented the general gradient approximation (GGA) excluding and... more A first-principles calculation implemented the general gradient approximation (GGA) excluding and including Hubbard U (GGA+U) is performed for the electronic and magnetic properties of the olivine phases LixFePO4 (0≤x ≤1). The calculated structural properties of the present study are in good agreement with experimental and other theoretical results. Total energy calculations show that an antiferromagnetic (AFM) state is more stable by the energy difference of 0.12 (x=0) and 0.03 eV/f.u. (x=1) than a ferromagnetic (FM) state. The present results are in consistent with experiments, in which AFM orderings of FePO4 and LiFePO4 were found below TN=125 K and at T N =50 K, respectively. The insertion/extraction of lithium affects slightly the spin moments of Fe, 3.96 (4.29) µB for FePO4 and 3.56 (3.77) µB for LiFePO4 from the GGA (GGA+U) approach. Consistent with observations, a different easy magnetization axes between x=0 (along a-axis) and 1 (along b-axis) reflects also the differences between their electronic structures, where the e g state is found to be a crucial. Both GGA and GGA+U approaches are valid to describe the valence electronic structure, but only the utilization of GGA+U is able for the conduction bands, in resulting appropriate solution for the band gaps. We also predict that partially intercalated single crystals (x=0.25, 0.5, and 0.75), which were synthesized at high temperature recently as solid solutions, are compensated half-metallic regardless of the exchange-correlation approaches.

RSC Advances, 2017

The distribution of oxygen functional groups on the surface of graphene oxide (GO) has been inves... more The distribution of oxygen functional groups on the surface of graphene oxide (GO) has been investigated experimentally and theoretically. Atomic layer deposition of TiO x was used to clarify the location of oxygen functional groups. We found that the oxygen functional groups are distributed in the form of islands, which is confirmed using aberration corrected transmission electron microscopy and X-ray photoelectron spectroscopy. The density functional studies further support these findings. The evolution of oxygen functional groups was also investigated with GO treated at 150, 200, 250, and 300 C. In addition, the reduction of epoxide and hydroxyl groups on the GO surface at different temperatures has been discussed in connection with ab initio molecular dynamics simulations.

Ceramics International, May 1, 2023

Defect and Diffusion Forum, Apr 17, 2023

We have presented the results of detailed studies of oxygen vacancy and niobium (Nb) substituted... more We have presented the results of detailed studies of oxygen vacancy and niobium (Nb)
substituted spinel Li4Ti5O12 (LTO) materials using the first-principles method within the framework of the density functional theory (DFT). We have shown that the ground state of oxygen vacancy and Nb-substituted LTO is paramagnetic (PM), and the Nb substitution is most stable on the 16d sites of both the Li and Ti ions. Our results indicate that the Nb substitution in the 16d site of Li-ion becomes the n-type metallic material. But the oxygen vacancy containing NbT i substituted LTO is changed from the p-type to the n-type, as increased concentration of Nb ions.