Quantum Chemical Molecular Dynamics Method Research Articles

A fundamental study of Fe–Cr binary alloy–oxide film interfaces at 288 °C by computational chemistry calculations

A quantum chemical molecular dynamics method was used in order to understand the oxide film degradation mechanism at metal/metal–oxide interfaces. The present study shows that oxygen diffusivity in the metal is significantly higher at a Fe–Cr/Fe 2O 3 interface compared to a Fe–Cr/Cr 2O 3 interface. This indicates that Cr 2O 3 enables protection of the surface for a longer period of time than Fe 2O 3 in a high temperature environment. Applied tensile strain enhances the oxygen mobility towards the metal surface. This process helps to increase the oxidation of the metal surface by forming metal oxygen bonds. Atomic charge analysis reveals that the oxygen atoms are negatively charged and the chromium atoms are more highly positively charged than iron ones. The negatively charged oxygen atoms are able to make covalent bonds with the positive metal atoms. This charge transfer process facilitates the formation of metal–oxygen bonds and weakens the metallic bonds.

Large-scale Quantum Chemical Molecular Dynamics Study on CO Oxidation Reaction on Precious Metal Surface

To study atomistic behavior of CO oxidation reaction on Pt(332) surface, we used ultra accelerated quantum chemical molecular dynamics method. First, we estimated the CO oxidation reactivity on step and terrace site of Pt(332) surface. Then, we confirmed that the effect of PtO2 stripe on step site on reactivity of the CO oxidation. It is shown that ultra accelerated quantum chemical molecular dynamics method is available for the analysis of reaction dynamics on metal surface. [DOI: 10.1380/ejssnt.2010.272]

S1106-1-6 ダイヤモンドライクカーボンの低摩擦メカニズムの量子分子動力学法を用いた検討([S1106-1]機能表面・機能界面の創成と評価)

S1106-1-6 ダイヤモンドライクカーボンの低摩擦メカニズムの量子分子動力学法を用いた検討([S1106-1]機能表面・機能界面の創成と評価)

Multi-scale theoretical study of support effect on sintering dynamics of Pt

The capability of theoretical durability studies to offer an efficient alternative methodology for predicting the potential performance of catalysts has improved in recent years. In this regard, multi-scale theoretical methods for predicting sintering behavior of Pt on various catalyst supports are being developed. Various types of Pt diffusions depending on support were confirmed by the micro-scale ultra accelerated quantum chemical molecular dynamics (UA-QCMD) method. Moreover, macro-scale sintering behavior of Pt/γ-Al 2O 3, Pt/ZrO 2 and Pt/CeO 2 catalysts were studied using a developed 3D sintering simulator. Experimental results were well reproduced. While Pt on γ-Al 2O 3 sintered significantly, Pt on ZrO 2 sintered slightly and Pt on CeO 2 demonstrated the highest stability against sintering.

A Theoretical Study of Initial Deposition Processes of Mg on MgO: A Novel Quantum Chemical Molecular Dynamics Approach

Initial deposition processes of Mg on MgO were studied using our novel quantum chemical molecular dynamics (QCMD) simulator. This novel simulator was developed on the basis of our tight-binding quantum chemical molecular dynamics (TB-QCMD) simulator and our molecular dynamics simulator. The justification of the novel QCMD simulator was shown by the excellent agreement of the QCMD result with the first-principles results and experimental results for the physicochemical properties of the MgO crystal. Dynamic behaviors of Mg atom deposited on the MgO(001) and (111) surfaces were simulated by the novel QCMD method. It was shown that the mobility of Mg deposited on the MgO(001) surface was larger than that on the (111) surface, which suggests the difference between the interaction of the deposited Mg atom with the MgO(111) surface and that with the MgO(001) surface.

Development of a Multi-Scale Electromigration Simulator Based on a Combination of Ultra Accelerated Quantum Chemical Molecular Dynamics and Kinetic Monte Carlo Methods Application to Cu Interconnects Lifetime Simulation

We present a novel study on electromigration (EM) phenomena in Cu interconnects using a newly developed multi-scale simulator that consists on a combination of a device scale simulator based on a kinetic Monte Carlo (KMC) method and an atomic scale simulator based on ultra accelerated quantum chemical molecular dynamics (UA-QCMD). We have firstly demonstrated the simulation of the lifetime of Cu interconnects using the newly developed device scale simulator setting some suitable KMC probabilities for the void movement according to the regions in which it can be divided, i.e., the crystal grain and the grain boundary. The simulated values are shown to be in good agreement with experimental values. In an attempt to connect the device scale studies to quantum chemical instances of the system – since the correlation of probability of the void movement with, for example, activation energies or diffusion coefficients is important – we have developed an atomic scale simulator based on our original UA-QCMD method. In this atomic scale simulation, the electron wind force was evaluated using our original electrical conductivity prediction simulator based on KMC method which uses the electronic states from tight-binding quantum chemical (TBQC) calculation. Using this atomic scale simulator under the conditions of 475 K of temperature and 2.5 ×1010 A/m2 of current density, we were able to successfully simulate the migration of a Cu atom from a lattice site to a vacant site by evaluating the electron wind force.

123 SCF-Tight-Binding量子分子動力学法によるトライボケミカル反応ダイナミクスシミュレーション(OS1.固体物理/流体物理のマルチフィジックス/マルチスケール解析(7),オーガナイズドセッション)

Our original SCF-Tight-Binding quantum chemical molecular dynamics method was applied to the tribochemical reaction dynamics of the additives in the automotive engine oil. We successfully elucidated the chemical reaction dynamics of the Zn-DTP and Mo-DTC additives under the friction condition. Both the formation dynamics and function of the Zn-DTP and Mo-DTC tribofilm were investigated and the effects of both the friction and the nascent Fe surface on the chemical reaction dynamics were well clarified on electronic- and atomic-scale.

Development of A Seebeck Coefficient Prediction Simulator Using Tight-Binding Quantum Chemical Molecular Dynamics

Technologies oriented to the development of thermoelectric materials are of great interest because they can assist in directly tapping the vast reserves of currently underused thermal energy. To improve the rational design of high-performance thermoelectric materials, a new numerical procedure for prediction of Seebeck coefficient based on the electronic information from tight-binding quantum chemical molecular dynamics method, has been developed. The newly developed simulator can evaluate Seebeck coefficient theoretically. The simulator is used for the prediction of the Seebeck coefficients for Pt and Si that are the representative materials for metals and semiconductors, respectively. The results show that both coefficients are in quantitative agreement with experimental data, i.e. in the case of Pt metal the predicted value is 5.62 µV/K while the experimental is -4.45 µV/K. Similarly, in the case of Si semiconductor the predicted value is -324.48 µV/K while the experimental is 300–400 µV/K. This new developed simulator can be used to guide the rational design of high performance thermoelectric materials.

Development of Constraint Algorithm for the Number of Electrons in Molecular Orbitals Consisting Mainly 4 f Atomic Orbitals of Rare-Earth Elements and Its Introduction to Tight-Binding Quantum Chemical Molecular Dynamics Method

Our original tight-binding quantum chemical molecular dynamics code, “Colors”, has been successfully applied to the theoretical investigation of complex materials including rare-earth elements, e.g., metal catalysts supported on a CeO2 surface. To expand our code so as to obtain a good convergence for the electronic structure of a calculation system including a rare-earth element, we developed a novel algorithm to provide a constraint condition for the number of electrons occupying the selected molecular orbitals that mainly consist of 4 f atomic orbitals of the rare-earth element. This novel algorithm was introduced in Colors. Using Colors, we succeeded in obtaining the classified electronic configurations of the 4 f atomic orbitals of Ce4+ and reduced Ce ions in a CeO2 bulk model with one oxygen defect, which makes it difficult to obtain a good convergence using a conventional first-principles quantum chemical calculation code.

Theoretical Simulation of Dielectric Breakdown by Molecular Dynamics and Tight-Binding Quantum Chemistry Methods

A novel methodology is addressed and employed to simulate dielectric breakdown process of the amorphous SiO2 (a-SiO2) under high electric fields, as well as the role of hydrogen and oxygen vacancy in the breakdown process. This methodology is based on classical molecular dynamics in conjunction with our original tight-binding quantum chemical molecular dynamics method. It is shown from the electronic structure that gap of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for a-SiO2 under no electric field at 300 K is calculated to be 7.5 eV and the orbital contributions to the valence band and conduction band are in line with experimental data. We have evaluated the electric field dependence of breakdown for a-SiO2 at 300 K and found that the insulator property shifts to conductor when electric field reached to a very high value of 5×1010 V/m. The result of this process can be ascribed to the decreasing of band gap induced by the destruction of geometry of a-SiO2 under very high electric field. Our results reveal that the conductivity of a-SiO2 increases with the increase of hydrogen or oxygen vacancy concentration in the oxide structure under the electric field. This supports the fact that defects play an important role in triggering breakdown process. Finally, a complex model has been build and used to simulate the influence of interface structure of Si and SiO2 under high electric field.

Novel computational chemistry approaches for studying physico-chemical properties of zeolite materials

Computational chemistry has made tremendous impact on the development of zeolite materials. Molecular dynamics (MD), Monte Carlo (MC), quantum chemistry (QC), and quantum chemical molecular dynamics (QCMD) methods have been applied to the studies of diffusion processes, adsorption characteristics, catalytic reaction mechanism, synthesis processes, acidic properties, etc. in zeolite materials. However, these traditional approaches are not able to accommodate complicated realistic systems because of their approximations and of the limitation of calculation models. To establish a novel computational chemistry approach for exploring new physico-chemical properties of zeolite materials, we have developed a novel dual ensemble MD (DEMD) program and original tight-binding QCMD program, ‘Colors’. The DEMD program can perform the permeation and separation dynamics simulation considering the gradient of chemical potential in a simulation cell. Colors program is over 5000 times faster than the traditional first-principles QCMD simulator. Hence, it enables us to employ more realistic large-scale models. Furthermore, we have also performed large-scale QC calculations based on the density functional theory (DFT) with a whole unit cell model of a zeolite material considering the periodic boundary condition (PBC). In this review, we put forward the application of our novel theoretical approaches for studying physico-chemical properties of zeolite materials.

Investigation of the dissociative adsorption for cyclopropane on the copper surface by density functional theory and quantum chemical molecular dynamics method

The dissociative adsorption of cyclopropane on the copper surface was studied using quantum chemical molecular dynamics method with “Colors-Excite” code and density functional theory by Amsterdam Density Functional program (ADF2000). The excited state of cyclopropane was used as adsorbate to simulate the dissociated adsorption under an irradiation energy of ca. 10 eV. One of the C–C bonds in cyclopropane was broken and the two new bonds between cyclopropane and copper surface were formed. The electrons transferred from the copper atoms to cyclopropane with a value of about 0.2 e. The shorter distances between the carbons and surface copper atoms showed the existence of strong interaction. Consistently, the results indicated metallacyclopentane was the most possible intermediate species in dissociative adsorption by ADF2000 and “Colors-Excite” method.

Tribochemical Reaction Dynamics of Phosphoric Ester Lubricant Additive by Using a Hybrid Tight-Binding Quantum Chemical Molecular Dynamics Method

To study the atomistic behavior of the phosphoric ester molecule on the nascent Fe surface under boundary lubrication conditions, we adopted a hybrid tight-binding quantum chemical molecular dynamics method. First, we investigated chemical interactions between phosphoric ester and the nascent Fe surface. Phosphoric ester was shown to interact with the nascent Fe surface, forming both covalent and ionic bonds. Formation and dissociation dynamics of covalent bonds during tribochemical reaction was clearly observed during the simulation. The effect of friction condition on the tribochemical reaction dynamics was then studied, and it was indicated that friction would influence the formation and the dissociation of covalent bonds. By using a hybrid tight-binding quantum chemical molecular dynamics method, we obtained insights on initial tribochemical reaction processes for the formation of tribofilm from the phosphoric ester molecule on the nascent Fe surface.

Development of Hybrid Tight-Binding Quantum Chemical Molecular Dynamics Method and Its Application to Boron Implantation into Preamorphized Silicon Substrate

The precise control of the thickness of amorphous layers and concentration of dopant atoms in thin layers is important for the fabrication of ultrashallow highly doped junctions. It was reported that amorphous layers suppress the channeling tail of implanted boron atoms. In this work, we studied the dynamics of boron implantation into a silicon substrate preamorphized by Ge irradiation, using our novel hybrid tight-binding quantum chemical molecular dynamics method. We have implemented a dynamic hybridization method in our study of preamorphization and implantation, in which a focused atom changes its position with simulation time. In the developed dynamic hybridization method, the region treated by the quantum chemistry method can dynamically change with simulation time. We have successfully applied the developed method and observed that the decrease in the kinetic energy of the implanted boron atom is correlated with the formation of chemical bonds between the implanted boron atom and the surrounding silicon atoms.

Development of SCF-Tight-Binding Quantum Chemical Molecular Dynamics Method and Its Application to Polymer Electrolyte Fuel Cell

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Tight-Binding Quantum Chemical Molecular Dynamics Study on First Proton Transfer Process of ORR Catalyzed by Cobalt-Porphyrin Complex

We investigated oxygen reduction reaction (ORR) dynamics catalyzed by cobalt-porphyrin using our original novel tight-binding quantum chemical molecular dynamics method. First, we determined parameters for tight-binding calculation based on first-principles parameterization. We have successfully simulated a first proton transfer process of the oxygen reduction reaction with the explicit consideration of surrounding water molecules. The transferred proton formed hydrogen bonding with a water molecule and conformational change of the OOH species was observed. It was proved that our tight-binding quantum chemical molecular dynamics method is effective for the investigation of oxygen reduction reaction dynamics in large complex system.

Combinatorial computational chemistry approach of tight-binding quantum chemical molecular dynamics method to the design of the automotive catalysts

Recently, we have developed a new tight-binding quantum chemical molecular dynamics program “Colors” for combinatorial computational chemistry approach. This methodology is based on our original tight-binding approximation and realized over 5000 times acceleration compared to the conventional first-principles molecular dynamics method. In the present study, we applied our new program to the simulations on various realistic large-scale models of the automotive three-way catalysts, ultrafine Pt particle/CeO 2(111) support. Significant electron transfer from the Pt particle to the CeO 2(111) surface was observed and it was found to strongly depend on the size of the Pt particle. Furthermore, our simulation results suggest that the reduction of the Ce atom due to the electron transfer from the Pt particle to the CeO 2 surface is a main reason for the strong interaction of the Pt particle and CeO 2(111) support.

Tight‐Binding Quantum Chemical Molecular Dynamics Method: a Novel Approach to the Understanding and Design of New Materials and Catalysts

Abstract Computational chemistry has made tremendous impact on the development of a variety of new materials including catalysts, semiconductors, ceramics, polymers, functional materials, etc. Traditionally, first-principles calculations were employed to clarify the chemical reactions on electronic and atomic level, which is essential for the materials and catalysts design. However, this method cannot simulate the chemical reaction dynamics at reaction temperatures, which is crucial fault and defect for more precise and accurate design to establish next-generation nanotechnology. Recently, first-principles quantum chemical molecular dynamics (QCMD) approach is expected to solve the above problem, however it can simulate very small system because it requests huge computational costs. Hence, recently we have succeeded in developing a tight-binding quantum chemical molecular dynamics (TB-QCMD) program, “Colors”, based on our original tight-binding theory. This method realizes over 5000 times acceleration in calculation time, compared to the conventional first-principles molecular dynamics method. To realize high accuracy in spite of the above high calculation speed, all the parameters for “Colors” were determined on the basis of first-principles density functional calculations. Thus, this novel TB-QCMD program was used successfully and effectively to investigate chemical reaction dynamics of large simulation models at reaction temperatures. In this review, we put forward the application of this newly developed code for the design of novel materials and catalysts systems.

Tight-Binding Quantum Chemical Molecular Dynamics Study on Depth Profile Prediction in Low Energy Boron Implantation Process

Creation of shallow junction for the future generation LSI is a crucial step in semiconductor industry and low-energy boron implantation process is considered to be a key technology. In this study, we have statistically investigated the effects of orientation of implantation on the dynamic behavior of boron implantation process into hydrogen-terminated Si(001) 2×1 surface by using our original tight-binding quantum chemical molecular dynamics method, which is over 5,000 times faster than conventional first-principle molecular dynamics method. It was found that depth profile of boron implantation can be controlled by orientation of boron implantation and the shallowest implantation depth was obtained in the case of tilt angle equal to 7° among the investigated tilt angles of 0°, 7°, 15°, 22.5°, 30° and 45° at the initial boron energy of 100 eV. At the boron implantation process of over 1 keV energy the tilt angle of 7° has been employed experimentally and the same tilt angle was predicted to be the best even at low-energy region of 100 eV. Furthermore, we investigated the effect of rotation angle on the depth profile and at all the investigated tilt angles the average implantation depth becomes shallower for rotation angle of 45° that is along <011> direction, than for rotation angle of 0° that is along <001>. Hence, the shallowest depth profile was obtained in the case of tilt angle of 7° and rotation angle of 45°, where the distribution of intruded boron atom was more concentrated than for the same tilt angle but rotation angle of 0°. The effect of tilt and rotation angles on the boron implantation process has not been clarified experimentally at low-energy boron implantation process of less than 1 keV and hence we concluded that theoretical optimization of low-energy boron implantation process has been succeeded by means of our original tight-binding quantum chemical molecular dynamics method.

Tight-binding quantum chemical molecular dynamics method: a novel approach to the understanding and design of new materials and catalysts

Computational chemistry has made tremendous impact on the development of a variety of new materials including catalysts, semiconductors, ceramics, polymers, functional materials, etc. Traditionally, first-principles calculations were employed to clarify the chemical reactions on electronic and atomic level, which is essential for the materials and catalysts design. However, this method cannot simulate the chemical reaction dynamics at reaction temperatures, which is crucial fault and defect for more precise and accurate design to establish next-generation nanotechnology. Recently, first-principles quantum chemical molecular dynamics (QCMD) approach is expected to solve the above problem, however it can simulate very small system because it requests huge computational costs. Hence, recently we have succeeded in developing a tight-binding quantum chemical molecular dynamics (TB-QCMD) program, “Colors”, based on our original tight-binding theory. This method realizes over 5000 times acceleration in calculation time, compared to the conventional first-principles molecular dynamics method. To realize high accuracy in spite of the above high calculation speed, all the parameters for “Colors” were determined on the basis of first-principles density functional calculations. Thus, this novel TB-QCMD program was used successfully and effectively to investigate chemical reaction dynamics of large simulation models at reaction temperatures. In this review, we put forward the application of this newly developed code for the design of novel materials and catalysts systems.