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解决方案
Solution
摘要:
BIOVIA Materials Studio CASTEP是一个从头算量子力学程序,利用密度泛函理论(DFT)来模拟各种材料类别的固体、界面和表面的性质,如陶瓷、半导体和金属。第一性原理计算使研究人员能够在不需要任何实验输入的情况下研究系统的电子、光学和结构特性的性质和起源。因此,CASTEP工作室非常适合于固体物理、材料科学、化学和化学工程等缺乏经验模型和实验数据的研究问题。在这些领域,研究人员可以使用计算机模拟来进行虚拟实验,从而大大节省了昂贵的实验费用,缩短了发育周期。
WHAT DOES BIOVIA MATERIALSSTUDIO CASTEP DO?
Researchers in chemistry and materials science may be tasked with a number of challenging goals like the development of new compounds, such as a stronger light-weight alloy or a semiconductor that will make a faster computer chip; or they may need to improve a manufacturing process that uses atomic layer deposition; or they may be faced with simply understanding and describing fundamental processes, explaining why one particular material is better than another. Modeling can address all of these challenges, provided that the method is fast, accurate, and works at the atomic scale.
Materials Studio CASTEP is just such a method. Originally developed in the Theory of Condensed Matter Group at Cambridge University, UK, Materials Studio CASTEP uses quantum mechanical calculations to study problems in chemicals and materials research. A large number of academic and commercial partners assures that the program incorporates the latest technologies and has been well-validated for the types of problems faced by research scientists in the fields mentioned above.
Materials Studio CASTEP is able to predict the structure of a material as well as many essential properties. In particular, it can predict electronic properties such as band gaps and Schottky barriers; optical properties such as phonon dispersion curves, polarizability and dielectric constants; or physical properties such as elastic constants. Put these all together to get a tool for the rapid and accurate design of new materials in silico.
Key features include a transition state search algorithm that greatly facilitates determination of reaction profiles and energy barriers, essential to an understanding of kinetics. The full 6x6 tensor of the elastic constants can be predicted for a periodic structure of any symmetry. Recent advances in the ability to compute phonon frequencies makes it possible to predict thermodynamic properties such as free energy and heat capacity for any material. Moreover, the ability to make thermodynamic predictions of solid-state systems enables the simulation of many condensed matter properties such as the phase stability of structural modifi cations.
Based on total energy pseudopotential methods, Materials Studio CASTEP requires as input only the number and type of atoms in a system and predicts properties such as lattice constants, molecular geometry, elastic constants, bandstructures, density-of-states, charge densities and wave functions,and optical properties.The pseudopotential planewave technology underlying Materials Studio CASTEP is well validated, with hundreds of scientific publications written each year demonstrating new applications of the code. Efficient parallel versions of the code are also available for large systems involving hundreds of atoms. Materials Studio CASTEP has been applied to a wide range of research problems such as surface chemistry, physiand chemisorption, heterogeneous catalysis, defects in semiconductors, grain boundaries, stacking faults, nanotechnology, molecular crystals, polymorphic studies, diffusion mechanisms, and molecular dynamics of liquids.
THE MATERIALS STUDIO ADVANTAGE
Materials Studio CASTEP is part of the Materials Studio®software environment. Materials Studio provides a user-friendly interface, complying with Windows? standards. Materials Visualizer, the core Materials Studio product, off ers a wide range of model building and visualization tools that allow you to construct rapidly models of the systems of interest, easily select the Materials Studio CASTEP module, and run an advanced quantum mechanical calculation. The simple user interface together with BIOVIA’s training programs ensure that even new users will be able to use the program with confidence.
A flexible client-server architecture means that calculations can be run on servers located anywhere on your network. Results are returned to your PC, where they may be displayed and analyzed. You can easily produce high-quality graphics of geometric structures, molecular orbitals, electrostatic potentials, or charge densities. Structures, graphs, and other data such as video clips produced from Materials Studio CASTEP output can be instantly exchanged with other PC applications, assisting you when sharing them with colleagues or when analyzing your results using spreadsheets and other packages.
HOW DOES BIOVIA MATERIALS STUDIO CASTEP WORK?
Materials Studio CASTEP 1-3 uses a total energy plane-wave pseudopotential method. In the mathematical model of the material, Materials Studio CASTEP replaces core electrons with effective potentials acting only on the valence electrons in the system. Electronic wave functions are expanded through a plane-wave basis set, and exchange and correlation effects can be included within either the local density (LDA) or generalized gradient (GGA) approximations. Combining the use of pseudopotentials and plane wave basis sets enables extremely efficient geometry optimizations of molecules, solids, surfaces, and interfaces. The primary reason that Materials Studio CASTEP has become so powerful is that the numerical methods used to solve the underlying quantum mechanical calculations are both computationally effi cient and extremely accurate.
Materials Studio CASTEP is capable of computing many electronic and optical properties using density functional perturbation theory (DFPT), also known as the linear response method. This approach makes possible a wider variety of properties than are possible using the so-called finite difference approaches, which require repeated computations on a series systems. Using DFPT, Materials Studio CASTEP can predict a number of significant observables including the phonon density of states, phonon dispersion, optical polarizability, IR spectra, and dielectric functions.
FEATURES AND CAPABILITIES
Calculation Tasks
• Total energies, forces, and stresses
• Many exchange-correlation functionals including B3LYP, and shape preserving optimization
• Geometry optimizations (including unit cell parameters)
• Molecular dynamics using NVE, NVT, NPH, and NPT ensembles
• Transition state search based on the linear and quadratic synchronous transit methodology (LST/QST)
• Elastic constants
• Phonon frequencies using linear response or finite displacements.
General Capabilities
• Choice of local, gradient-corrected, and nonlocal functionals for approximating exchange and correlation effects
• Nonlocal functional include screened-exchange, HF, B3LYP and PBE0
• LDA+U method for strongly correlated systems, including magnetic systems
• Semi-empirical dispersion correction schemes
• Ultra soft and norm-conserving pseudopotentials for the entire periodic table
• Tkachenko-Scheffler parameters for dispersion corrected DFT
Job Control Options
• Choice of parallelization strategy to optimize computational performance
• Choose number of CPU's
• Specify server machine
• Monitor output and status reports including text or graphs of energy and gradient during geometry optimization
• Live updates of the model geometry and job status
• Halt jobs on remote server via the Materials Visualizer
Properties
• Band structures
• Core-level spectra8 like EELS, ELNES or XES
• Dielectric function polarizability, refl ectivity
• Electron work function
• IR spectra8
• Mulliken population analysis for atoms and bonds
• Optical properties: frequency dependent
• Phonon dispersion
• Raman spectra8
• Refractive index, UV spectra8
• Static elastic constants
• Thermodynamic properties in quasiharmonic approximations (free energy, enthalpy, entropy, heat capacity, Debye temperature)
• Total and projected phonon density of states
• Orbital-resolved population analysis
Graphical Displays with Materials Studio Visualizer
• 3-D contours and 2-D slices
• Charge, spin, and deformation densities
• Fermi surface
• Overlay multiple plots and color surfaces by property maps
• Simulated scanning tunneling microscopy (STM) images
Miscellaneous Options
• Real or reciprocal space pseudopotential representation
• Full use of space-group symmetry
• Multiple options for accelerating SCF convergence:DIIS, density mixing, smearing.
REFERENCES
1. S. J. Clark, M. D. Segall, C. J. Pickard, P. J. Hasnip, M. J. Probert, K. Refson, M. C. Payne Zeitschrift für Kristallographie, 2005, 220(5-6) pp.567-570
2. Payne, M. C. , Teter, M. P., Allan, D. C, Arias, T. A., and Joannopoulos, J. D., Rev. Mod. Phys., 1992, 64, 1045.
3. M. D. Segall, P. J. D. Lindan, M. J. Probert, C. J. Pickard, P. J. Hasnip, S. J. Clark, M. C. Payne, J. Phys.: Cond. Matt., 2002, 14, 2717.
4. Halgren, T. A. and Lipscomb, W. N., Chem. Phys. Lett., 1997, 49, 225.
5. Bell, S. and Crighton, J. S., J. Chem. Phys., 1984, 80, 2464.
6. Fischer, S. and Karplus, M., Chem. Phys. Lett., 1992, 194, 252.
7. N. Govind, M. Petersen, G. Fitzgerald, D. King-Smith, and J. Andzelm, Computational Materials Science, 2003, 28, 250.
8. V. Milman K. Refson, S.J. Clark, C.J. Pickard, J.R. Yates, S.-P. Gao, P.J. Hasnip, M.I.J. Probert, A. Perlov, M.D. Segall Journal of Molecular Structure: THEOCHEM 2010, 954, 22
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