Quantum Chemical Molecular Dynamics Program Research Articles

Quantum Chemistry Study on Absorption Spectra, Electronic and Electrical Properties of Organic Dye on Anatase(001)

As the most reactive surface, the stoichiometric O-bridge terminated anatase(001) surface attracted considerable attentions in many application fields. The interfacial electron transfer in dye-sensitized anatase(001) plays a principal role in a variety of photoinduced reactions. In the present work, the UV-vis absorption spectrum of TiO2 bulk and different surface models were calculated by means of tight-binding quantum chemical molecular dynamics program "Colors-excite" for the first time. The thickness dependence on electronic and electrical properties of anatase(001) surface was achieved. The anatase(001) surface with a thickness of 1.0 nm shows excellent electronic and electrical properties. Moreover, the most suitable binding mode (dissociative adsorption) and absorption spectra of perylene with acrylic acid (PAA) on the optimum anatase(001) were investigated. A significant red-shift was observed from the UV-vis absorption spectrum of PAA/anatase(001) system. The red-shift occurring when PAA adsorbed on anatase(001) surface suggests that PAA/anatase(001) may be potential candidate for dye-sensitized solar cell. This study also proposed an effective computational tool "Colors-excite" to study of the electronic excitation properties for both molecular and periodic systems.

Development of Multiscale Simulator for Dye-Sensitized TiO2 Nanoporous Electrode Based on Quantum Chemical Calculation

In this study, we have developed a novel multiscale simulator for a dye-sensitized TiO2 porous electrode. In the simulator, we can estimate the properties of the dye-sensitized TiO2 porous electrode using the three-dimensional mesoscopic structure model constructed on the basis of our original porous structure simulator. The microscopic physical properties of the materials were estimated by quantum chemistry calculation using a tight-binding quantum chemical molecular dynamics program. From the calculation results, we determined the absorption coefficient and the diffusion coefficient of excited carriers used in the macroscopic simulation for photoelectrode characteristics. By using this multiscale simulator, we will be able to determine the best electrode system efficiently.

Theoretical Study on the Electronic and Electrical Properties of p-Type Transparent Conducting Metal Oxides

Transparent conducting oxides (TCOs) continue to be in high demand because of their immediate applications. In addition to good quality n-type TCOs, there is increasing demand for good p-type TCOs. In the present study, we reported a theoretical study on the electronic and electrical properties for p-type TCO, Zn-doped In2O3 (IZO). The geometries of IZO were optimized using the density functional theory (DFT). Based on these optimized structures, the density of states, frontier molecular orbital contours, and electrical conductivity of IZO were calculated by combining the tight-binding quantum chemical molecular dynamics program, “Colors” and Monte Carlo method. The calculated band gap by “Colors” at G point is 2.87 eV, which is in good agreement with experimental value. In density of states of IZO, a shallow acceptor-type impurity level associate with Zn doping was observed above the top of the valence band. The frontier orbital analysis shows that the acceptor-type impurity level consists of O 2p and Zn 3d. On the other hand, the electrical conductivity and carrier mobility of IZO were evaluated. Comparing the electrical conductivity of IZO with that of its parent material In2O3, it was found that the electrical conductivity increased significantly when Zn-dopant was introduced to In2O3. The higher electrical conductivity of IZO was considered to be attributed to impurity state and therefore the p-type conductivity.

Development of a Thermal Conductivity Prediction Simulators Based on the Effects of Electron Conduction and Lattice Vibration

Estimation of the thermal conductivity for nano-materials based on quantum chemical methodologies provides important information for the development process of nano-scale devices, particularly those including impurities, defects, surfaces, and hetero-interfaces. Existing quantum mechanics-based methods for theoretically estimating the thermal conductivity of nano-materials are characterized by huge computational costs, which often prevent their applications to complex systems. Recently we have succeeded in the development of our original tight-binding quantum chemical molecular dynamics program “Colors”, which is able to realize calculations over 5000 times faster than conventional first principles molecular dynamics methods. Furthermore, based on a method that embeds “Colors” within a Monte Carlo paradigm we are able to compute values corresponding to carrier mobility, enabling thus the computation of electrical conductivity for different materials. Based on this system, in the present work, we describe a further development directed to the realization of two systems for thermal conductivity prediction. These systems of thermal conductivity prediction are based on two kinds of evaluation methods i) the estimation of the lattice vibration effect using classical molecular dynamics simulations and, ii) the conduction electron effect using the Wiedemann–Frantz law which is the basis of our recently proposed method for electrical conductivity prediction based on “Colors”. We have applied the methodology to evaluate the lattice vibration effect in amorphous SiO2, bolosilicate glass, cubic-ZrO2, and diamond while the electron conduction effect has been evaluated for metallic Ti, Sn.

Investigation of the photo-dissociation reactions for alkyl nitrite by quantum chemical molecular dynamics program “Colors-Excite”

The photodissociation of alkyl nitrites series (RONO) in gaseous state were studied using density functional theory with Amsterdam Density Functional program (ADF2000) and quantum chemical molecular dynamical method by “Colors-Excite” code. The different dissociative phenomena have been explained by this investigation. Alkyl nitrites were shifted to their excited states by capturing the light energy and the bonds of O–N (RO–NO) were broken. A two-step reaction occurred for methyl nitrite (THN) to yield the diverse products, such as RO radical, NO and HNO, whereas only one-step reaction occurred for tert-butyl nitrite (TBN). The consistent results in theoretical calculation and experiment, including geometrical structures and excitation energies, demonstrated the good performances of “Colors-Excite”.

Periodic density functional and tight-binding quantum chemical molecular dynamics study of catalytic properties on γ-Al 2O 3 supported Pt catalysts

We investigated the interactions of platinum metal clusters on the γ-alumina using a periodic density functional theory method. Results showed that electron transfer occurs between platinum metal clusters and γ-Al 2O 3. We also investigated NO adsorption properties (NO–Pt 4/γ-Al 2O 3) in order to clarify the support effect on NO activation in terms of the elongation of N–O bond length and NO molecular charge. In our results, the support increases NO activation for three-fold sites but decreases it for on-top and bridge sites. Moreover, the support changes the site preference of NO adsorption. In addition, in order to clarify the support effect at finite temperature, we studied the dynamic behaviors of supported precious metal catalysts by using a tight-binding quantum chemical molecular dynamics program named ‘Colors’.

Development of Electrical Conductivity Estimation Method Based on Tight-Binding Quantum Chemical Molecular Dynamics Simulation

In the development of materials for nano-scale devices, particularly those including impurities, defects, surfaces, and hetero-interfaces, estimation of their electrical conductivity based on quantum chemistry provides important information. Existing quantum mechanics-based methods for theoretically estimating the electrical conductivity require huge computational cost, which prohibit their applications to complex systems. We have already succeeded in the development of our original tight-binding quantum chemical molecular dynamics program “Colors”, which realizes a calculation speed over 5000 times faster than the conventional first principles molecular dynamics methods. Here we present a novel electrical conductivity estimation method based on “Colors” combined with Monte Carlo algorithm for estimating the value corresponding to the carrier mobility. We have applied the developed method to systems of C, Si, Ge, and Sn. Calculated results quantitatively agree with experimental data, which indicates the validity of the developed method. We have also applied the developed method to the study of Si surface.

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 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.

Large-scale calculations of solid oxide fuel cell cermet anode by tight-binding quantum chemistry method

Improvement of anode characteristics of solid oxide fuel cells is important for the better cell performance and especially the direct use of hydrocarbons. A mixture of ceramics and metal is generally used as anode, and different combinations of ceramics and metals lead to different electrode characteristics. We performed large-scale calculations to investigate the characteristics of Ni/CeO 2 and Cu/CeO 2 anodes at the electronic level using our tight-binding quantum chemical molecular dynamics program. Charge distribution analysis clarified the electron transfer from metal to oxide in both anodes. The calculations of density of states clarified different contributions of Ni and Cu orbitals to the energy levels at around Fermi level in each cermet. Based on the obtained results, we made considerations to explain different characteristics of both cermet anodes. The effectiveness of our approach for the investigation of complex cermet system was proved.

Tight-binding quantum chemical molecular dynamics simulation of boron activation process in crystalline silicon

The precise control of dopant atom is one of the most important challenges to fabricate ultra-shallow and highly doped junctions. In the present study, the activation process of B atom in Si crystal was investigated at low temperature of 500 °C by using our tight-binding quantum chemical molecular dynamics method, which is over 5000 times faster than the conventional first-principles molecular dynamics method. The simulation results indicate that the B atom diffuses through the interstitial sites in the Si crystal even at low temperature of 500 °C. Moreover, we found that the boron atom tends to migrate into the lattice vacancy and however the diffusion of the B atom is very hard after the boron atom is trapped in the single lattice vacancy. On the other hand, when there are two adjacent lattice vacancies in the Si crystal, the B atom migrates frequently between two adjacent vacancies back and forth. This result predicts that two adjacent lattice vacancies impede the B activation in the Si crystal. Finally, we confirmed that our tight-binding quantum chemical molecular dynamics program is very effective to elucidate the boron activation process in the Si crystal, considering the electronic states and electron transfer dynamics.

A theoretical study on the cyclopropane adsorption onto the copper surfaces by density functional theory and quantum chemical molecular dynamics methods

We report a theoretical study on the cyclopropane adsorption onto Cu(1 1 1) surfaces by density functional theory (DFT) and quantum chemical molecular dynamics methods. The equilibrium geometry of the physisorbed species was obtained using both periodic and cluster models by DFT methods that employ Cambridge serial total energy package (CASTEP), DMol ab initio quantum chemistry software of Accelrys’ materials studio (DMol), and Amsterdam density functional (ADF) program. It was found that the adsorbate molecule was tilted towards the metal surface with one CC bond (upwards) parallel to the surface and that the physisorption occurred via a third carbon atom pointing (downwards) towards the surface. The electronic distribution and geometrical structure of physisorbed cyclopropane were slightly deviated from its gas phase molecule. The calculated vibrational frequencies and adsorption energies are close to experimental data, confirming the reliability of our DFT results. The adsorption process was simulated using our novel tight-binding quantum chemical molecular dynamics program, ‘Colors’. The calculation results indicated that both the adsorption and desorption processes of cyclopropane took place molecularly. The electron transfer and structural properties of equilibrium position obtained by ‘Colors’ are consistent with those by the first principles DFT methods.

Combinatorial Computational Chemistry

A new methodology “Combinatorial Computational Chemistry” was proposed to realize theoretical high-throughput screening of materials. In this review, we introduced our recent successful applications of combinatorial computational chemistry to material design. Especially, we succeeded in the development of huge number of new simulation programs for combinatorial computational chemistry. For example, our SCF-tight-binding quantum chemical molecular dynamics program is very effective to realize high-throughput screening, since it realizes more than 5,000 times acceleration. Furthermore, we succeeded in the development of multi-physics quantum chemical molecular dynamics program based on our SCF-tight-binding theory, which can simulate multi-physics phenomena including chemical reaction, shear, impact, stress, flow, electric field and so on. This new program realizes various process design in addition to material design on the basis of the combinatorial computational chemistry. We emphasized here that our new simulation programs are very powerful tool to realize high-throughput screening for both material and process design, which cannot be accomplished by the traditional first-principles approach.

Quantum Chemical Molecular Dynamics Simulation of the Plasma Etching Processes

Recently, we reported the successful development of a new accelerated quantum chemical molecular dynamics program “Colors”, which is based on our original tight-binding theory. This methodology enables us to perform fast and accurate quantum chemical molecular dynamics simulations as compared to the conventional first principles molecular dynamics methods. In the present investigation, “Colors” program is used to simulate the bombardment of an energetic CF2 radical onto a SiO2 surface. Atomic bond populations were analyzed in order to clarify the bond-breaking and bond-formation processes during the bombardment. The results indicate that the bombardment of a CF2 radical with higher kinetic energy led to Si-O bond-breaking as well as to the formation of C-O and Si-F bonds. The results are in good agreement with experimental observations. Furthermore, it can also be deduced from this study that the novel accelerated quantum chemical molecular dynamics program is a very effective tool to clarify the chemical reaction dynamics during the plasma etching processes.

A Theoretical Study on the Realistic Low Concentration Doping in Silicon Semiconductors by Accelerated Quantum Chemical Molecular Dynamics Method

We present a theoretical study of the structural and electronic properties of a realistic low concentration (<0.5%) doping model in silicon semiconductor. The density of states was calculated using our newly developed accelerated quantum chemical molecular dynamics method, based on our original tight-binding theory. Using this approach, the band structures of large-size silicon model including n-type and p-type dopants were successfully simulated. The results are in good agreement with the experimental results. Furthermore, we also performed quantum chemical molecular dynamics simulation of the dopants in silicon and observed the change of the dopant levels during the simulation. These results clearly suggest that our original quantum chemical molecular dynamics program is a very effective tool for not only the band structure of a realistically low concentration dopant model but also for the electronic states dynamics of silicon semiconductors.

A Quantum Molecular Dynamics Simulation Study of the Initial Hydrolysis Step in Sol−Gel Process

The dynamic behavior of the hydrolysis reaction of Si(OCH3)4 under neutral, basic, and acidic conditions was investigated, for the first time, at the atomic level with short time intervals using a novel tight-binding quantum chemical molecular dynamics program “Colors”. The initial parameters required for the computation were determined completely on the basis of the first principles density functional calculations using Amsterdam density functional program. The simulation results of this study clearly indicate that a flank-side attack mechanism is favored, in all the three cases, for the hydrolysis process, and pentacoordinate silicon intermediates are easy pathways for the displacement of −OCH3 by −OH on silicon. Moreover, the presence of the acid or the base as catalyst promotes the hydrolysis by rapid formation of Si−OH bond in comparison to the hydrolysis under neutral condition. Furthermore, in the case of the latter condition, it was observed that the proton oscillates between −OH and −OCH3 before ...

Application of Accelerated Quantum Chemical Molecular Dynamics Method to the Electric and Electronics Engineering.

In addition to the theoretical prediction on the properties and functions of the electric and electronics materials, the simulation on the dynamic processes, such as etching process and chemical mechanical polishing process, are strongly demanded. Recently, we have succeeded in the development of a new accelerated quantum chemical molecular dynamics program, which is more than 5, 000 times faster than the regular first-principles molecular dynamics approach. This program enables us to calculate a realistic etching process, chemical mechanical polishing process, etc., employing large simulation model. In this review, we summarize the theory of our accelerated quantum chemical molecular dynamics and its application to various dynamic processes related to the electric and electronics engineering.

Tight-binding quantum chemical molecular dynamics study of cathode materials for lithium secondary battery

Our tight-binding quantum chemical molecular dynamics (TBMD) program was applied to the investigation of the structural and electronic properties of Li x Mn 2O 4. The calculated lattice constants of the LiMn 2O 4 and λ-MnO 2 were 8.17 and 8.08 Å, respectively, which are in good agreement with experimental results. The electronic analysis showed that the manganese atoms in the LiMn 2O 4 were separated into two groups based on their electronic states, which correspond to Mn 3+ and Mn 4+. We calculated the average potential for the reaction of Li+Mn 2O 4→LiMn 2O 4 and obtained the average potential of 4.2 V. The experimental value of the potential is approximately 4.0 V, indicating that our program is a powerful tool to predict the potential of various materials, as well as their atomistic and electronic structures.

Development of New Tight-Binding Molecular Dynamics Program to Simulate Chemical-Mechanical Polishing Processes

We developed a new accelerated quantum chemical molecular dynamics program called “Colors” which can simulate the chemical-mechanical polishing (CMP) processes. It is more than 5,000 times faster than the regular first-principles molecular dynamics program, since it is based on our original tight-binding theory. We employed a SiO2 particle as a polishing material. Two types of silicon surfaces, clean Si(100) and H-terminated Si(100) 2×1, were modeled to clarify the effect of the Si surface structure on the dynamic behaviors of the CMP processes. We paid attention to the bond population of the silicon atom during the CMP processes. The bond population of the silicon atom was decreased by the CMP process on both surfaces, indicating that the electronic state of the silicon wafer became unstable due to the CMP process. It is an interesting finding that the hydrogen atoms were desorbed from the H-terminated Si(100) 2×1 surface. The results indicate that our new program can simulate both the chemical reactions and mechanical polishing processes. To the best of our knowledge, this is the first simulator of the CMP processes on the atomic and electronic levels.