Ab-initio Study of the Interfacial Properties in Ultrathin MgO Films on O-rich FeO/Fe(001) Surfaces

전준진,유병덕 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.5

Using ab-initio simulations based on density functional theory, we systematically studied the interfacialproperties of MgO films on O-rich FeO/Fe(001) surfaces with increasing number of MgOlayers from one to three monolayers (MLs). The structural and the adhesion properties of theMgO/FeO/Fe(001) system were assessed and compared with those of simple MgO/Fe(001) interfaces. Our calculated results showed that the adhesion energy for MgO/FeO/Fe(001) was smallerthan that for simple MgO/Fe(001). An analysis of the electronic structures and the charge rearrangementsof the MgO/FeO/Fe(001) interfaces was also performed. The work functions of theMgO/FeO/Fe(001) systems upon the deposition of MgO films exhibited smaller decreases (0.45–0.67 eV) than those (1.43–1.74 eV) of the MgO/Fe(001) systems. In addition, the obtained workfunctions (3.77–3.99 eV) for MgO/FeO/Fe(001) were much larger than those (2.12–2.43 eV) forMgO/Fe(001).

Ab initio and kinetic Monte Carlo study of lithium diffusion in LiSi, Li₁₂Si₇, Li₁₃Si₅ and Li₁₅Si₄

Moon, J.,Lee, B.,Cho, M.,Cho, K. Elsevier Sequoia 2016 Journal of Power Sources Vol.328 No.-

The kinetics of lithium atoms in various Li-Si binary compounds are investigated using density functional theory calculations and kinetic Monte Carlo calculations. The values of the Li migration energy barriers are identified by NEB calculations with vacancy-mediated, interstitial and exchange migration mechanisms in crystalline LiSi, Li<SUB>12</SUB>Si<SUB>7</SUB>, Li<SUB>13</SUB>Si<SUB>4</SUB>, and Li<SUB>15</SUB>Si<SUB>4</SUB>. A comparison of these NEB results shows that the vacancy-mediated Li migration is identified as the dominant diffusion mechanisms in Li-Si compounds. The diffusion coefficients of Li in Li-Si compounds at room temperature are determined by KMC simulation. From the KMC results, the recalculated migration energy barriers in LiSi, Li<SUB>12</SUB>Si<SUB>7</SUB>, Li<SUB>13</SUB>Si<SUB>4</SUB>, and Li<SUB>15</SUB>Si<SUB>4</SUB> correspond to 0.306, 0.301, 0.367 and 0.320 eV, respectively. Compared to the Li migration energy barrier of 0.6 eV in crystalline Si, the drastic reduction in the Li migration energy barriers in the lithiated silicon indicates that the initial lithiation of the Si anode is the rate-limiting step. Furthermore, it is also found that Si migration is possible in Li-rich configurations. On the basis of these findings, the underlying mechanisms of kinetics on the atomic scale details are elucidated.

Ab-initio Study of Physical Properties of MgO/FeOx/Fe(001) Interfaces

박진우,유병덕,장영록 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.3

The effects of partially oxidized interfacial FeOx layers on the physical properties of MgO/FeOx/Fe(001) (x = 0, 0.25, 0.5, 0.75, 1) were studied using ab-initio calculations. The free energy calculations as a function of the O chemical potential ΔμO showed that the formation of the interfaces occurred in the order of p(1×1) MgO/Fe(001) (in the Mg-rich limit) → p(2×2) MgO/FeO0.25/Fe(001) → c(2×2) MgO/FeO0.5/Fe(001) → p(2×2) MgO/FeO0.75/Fe(001) → p(1×1) MgO/FeO/Fe(001) (in the O-rich limit) with increasing ΔμO. The electronic structures, the work functions, and the electron rearrangements for MgO/FeOx/Fe(001) interfaces were also investigated. These results indicate that the O contents x of FeOx at the interfaces between MgO and Fe can significantly affect the physical properties of the MgO/FeOx/Fe(001) interfaces.

<i>Ab initio</i> study of H, B, C, N, O, and self-interstitial atoms in hcp-Zr

You, Daegun,Ganorkar, Shraddha,Joo, Minsoo,Park, Donghyun,Kim, Sooran,Kang, Keonwook,Lee, Dongwoo ELSEVIER SCIENCE 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.787 No.-

<P><B>Abstract</B></P> <P>In this work, we investigate the stabilities of H, B, C, N, O, and Zr atoms at various interstitial sites in hcp-Zr using a first-principles theoretical approach. The formation energy of each interstitial atom at each site in the hcp crystal was determined, and the difference in the energy at different sites were considered as a static energy barrier to predict energetically favored diffusion pathways. Linear and non-linear prediction models for the interstitial formation energy were developed using readily accessible chemical and structural input parameters. We show that a simple linear model predicts the formation energies of the interstitial atoms with an R<SUP>2</SUP> of 97%.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Formation energies (E<SUB>f</SUB>) of H, B, C, N, O and Zr impurity atoms at various interstitial sites of hcp-Zr were determined. </LI> <LI> The most preferable diffusion path for each atom was predicted by considering the difference of E<SUB>f</SUB> at different sites. </LI> <LI> Simple linear and non-linear prediction models for E<SUB>f</SUB> were proposed. </LI> <LI> A linear model with four readily accessible input parameters predicts E<SUB>f</SUB> with R<SUP>2</SUP> of 97%. </LI> <LI> The key input parameters for E<SUB>f</SUB>: electronegativity, valence electrons, the interatomic distance, interstitial symmetricity. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Using a Scale-bridging Technique to Determine the Effect of Elastic Properties on Stress Distribution Around the Femoral Stem of an Artificial Hip Joint with a Simplified Geometry

C. U. Jeong,S.-C. Lee,H. N. Rhee,K. S. Park,S.-H. Choi 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.4

A scale-bridging technique was used to investigate the effect of the elastic properties of -Ti alloys on thestress distribution around the femoral stem of an artificial hip joint with a simplified geometry when underan external loading. The anisotropic elastic constants of single-crystalline -Ti alloys (TN1: Ti-18.75 at% Nb,TN2: Ti-37.5 at% Nb, and TN3: Ti-43.75 at% Nb) were calculated using an ab-initio technique that wasbased on density functional theory calculation. The single-crystalline elastic constants calculated via the abinitiotechnique were used to calculate the elastic constants of polycrystal -Ti alloys using an elastic selfconsistentscheme. Finite element analysis based on the elastic constants of polycrystalline -Ti alloys fora femoral stem was conducted to calculate the above-mentioned stress distribution. The model system consistingof a TN1 alloy exhibited a relatively high level of von Mises stress on the surface of cancellousand cortical bones compared to model systems consisting of TN2, TN3 alloys and commercial biomaterials(Ti-6Al-4V alloy and 316STS). The thickness of the cancellous bone between the femoral stem and thecortical bone affected the stress concentration on the surface of the cortical bone.

Magnetic, electric and magnetocaloric properties of EuFe0.5Mn0.5O3 perovskite: Monte Carlo study and ab-initio calculations

Imami M.,Masrour R. 한국세라믹학회 2024 한국세라믹학회지 Vol.61 No.1

Studies on the magnetic and electrical behavior of the perovskite complex EuMn0.5Fe0.5O3, which crystallizes in the orthorhombic structure and belongs to the symmetry group (Pbnm), have been conducted based on this study using numerical techniques More specifically, we investigated the magnetic and electrical properties of the EuMn0.5Fe0.5O3 material using approximations created within the framework of density functional theory, such as a full potential linearized augmented plane wave and the generalized gradient approximation. The magnetization, the transition temperature, as well as the fluctuation of the magnetic entropy, the specific heat, and the variation of the adiabatic temperature and relative cooling power. were analyzed using the Monte Carlo simulations when it was discovered via research that this compound exhibit spin-reorientation phenomena as it behaves like a conducting metal.

Interaction at the nanoscale of fundamental biological molecules with minerals

Valdre, Giovanni,Moro, Daniele,Ulian, Gianfranco Techno-Press 2013 Advances in nano research Vol.1 No.3

The availability of advanced nanotechnological methodologies (experimental and theoretical) has widened the investigation of biological/organic matter in interaction with substrates. Minerals are good candidates as substrates because they may present a wide variety of physico-chemical properties and surface nanostructures that can be used to actively condense and manipulate the biomolecules. Scanning Probe Microscopy (SPM) is one of the best suited techniques used to investigate at a single molecule level the surface interactions. In addition, the recent availability of high performance computing has increased the possibility to study quantum mechanically the interaction phenomena extending the number of atoms involved in the simulation. In the present paper, firstly we will briefly introduce new SPM technological developments and applications to investigate mineral surfaces and mineral-biomolecule interaction, then we will present results on the specific RNA-mineral interaction and recent basics and applicative achievements in the field of the interactions between other fundamental biological molecules and mineral surfaces from both an experimental and theoretical point of view.

A “turn-on” fluorescent microbead sensor for detecting nitric oxide

Yang, Lan-Hee,Ahn, Dong June,Koo, Eunhae Dove Medical Press 2015 INTERNATIONAL JOURNAL OF NANOMEDICINE Vol.10 No.-

<P>Nitric oxide (NO) is a messenger molecule involved in numerous physical and pathological processes in biological systems. Therefore, the development of a highly sensitive material able to detect NO in vivo is a key step in treating cardiovascular and a number of types of cancer-related diseases, as well as neurological dysfunction. Here we describe the development of a fluorescent probe using microbeads to enhance the fluorescence signal. Microbeads are infused with the fluorophore, dansyl-piperazine (Ds-pip), and quenched when the fluorophore is coordinated with a rhodium (Rh)-complex, ie, Rh<SUB>2</SUB>(AcO<SUP>−</SUP>)<SUB>4</SUB>(Ds-pip). In contrast, they are able to fluoresce when the transition-metal complex is replaced by NO. To confirm the “on/off” mechanism for detecting NO, we investigated the structural molecular properties using the Fritz Haber Institute <I>ab initio</I> molecular simulations (FHI-AIMS) package. According to the binding energy calculation, NO molecules bind more strongly and rapidly with the Rh-core of the Rh-complex than with Ds-pip. This suggests that NO can bond strongly with the Rh-core and replace Ds-pip, even though Ds-pip is already near the Rh-core. However, the recovery process takes longer than the quenching process because the recovery process needs to overcome the energy barrier for formation of the transition state complex, ie, NO-(AcO<SUP>−</SUP>)<SUB>4</SUB>-(Ds-pip). Further, we confirm that the Rh-complex with the Ds-pip structure has too small an energy gap to give off visible light from the highest unoccupied molecular orbital/lowest unoccupied molecular orbital energy level.</P>

Theoretical Study of Scanning Probe Microscope Images of VTe2

Sung Soo Park,Jeeyoung Lee,Wang Ro Lee,Kee Hag Lee* 대한화학회 2007 Bulletin of the Korean Chemical Society Vol.28 No.1

Ab initio periodic Hartree-Fock calculations with the full potential and minimum basis set are applied to interpretation of scanning tunneling microscope (STM) and atomic force microscope (AFM) images on 1T-VTe2. Our results show that the simulated STM image shows asymmetry while the simulated AFM image shows the circular electron densities at the bright spots without asymmetry of electron density to agree with the experimental AFM image. The bright spots of both the STM and AFM images of VTe2 are associated with the surface Te atoms, while the patterns of bright spots of STM and AFM images are different.

Hydrogen bond dynamics in liquid water: Ab initio molecular dynamics simulation

김철희,염민선,김은애 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.1

The effect of intermolecular interaction on the distribution of the harmonic vibrational frequencies of water molecules was investigated through ab initio molecular dynamics simulations based on the Born-Oppenheimer approach. For single water, the effect of the dynamics of the oxygen atom in single water and the simulation time step on the frequency distribution were examined. The distributions of the OH stretching and HOH bending vibrational frequencies of liquid water were compared to those of single water. The probability distributions of the change in OH bond length and the lifetime of the dangling OH bond were also obtained. The distribution of the frequencies was strongly affected by the long lifetime of the dangling OH bond, resulting in the formation of hydrogen bonds between water molecules.