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Unformatted text preview: NC STATE CHE596M MultiScale Modeling of Matter Instructor: Keith E. Gubbins Lecture 12: General Features of Atomistic Simulation NC STATE Outline • General features of atomistic simulation • Brief description of MC and MD • Features common to MC and MD • Difficult systems • Differences between MC and MD • The Monte Carlo method NC STATE Atomistic Simulation Methods  General Features • References : – A. R. Leach, Molecular Modelling , 2 nd ed., Ch. 6, 8, Prentice Hall (2001) – D. Frenkel and B. Smit, Understanding Molecular Simulation , 2 nd ed., Academic Press (2002) – M. P. Allen and D. J. Tildesley, Computer Simulation of Liquids , Clarendon Press, Oxford (1987) – K. E. Gubbins and N. Quirke, Molecular Simulation and Industrial Applications , Chapter 1, Gordon and Breach (1996) NC STATE Atomistic Simulation Methods  General Features • In these methods the equations of statistical mechanics are solved numerically. The two principal methods are Monte Carlo (MC) and Molecular Dynamics (MD) • In atomistic (molecular) simulation we must first specify the molecular model: For fluids this consists of specifying equations for the intermolecular forces, intramolecular forces, molecular mass For some heterogeneous systems, e.g. colloids, composites, fluidsolid systems, we often need to specify, in addition, the space coordinates of solid atoms, and this becomes part of the model • The equations of statistical mechanics are then solved ‘exactly’, without further approximation NC STATE • Uses : 1. Test model by comparing simulated and experimental properties. Then use model in further simulations to carry out “experiments” not possible in the laboratory, e.g. critical points for molecules that decompose below T c , properties of molten salts, longchain hydrocarbon properties at very high pressures, properties of confined nanophases, etc. 2. Fundamental studies, e.g. to determine range of validity of Kelvin’s equation, Fick’s law of diffusion, Newton’s law of viscosity, etc. 3. Test theories by comparing theory and simulation Atomistic Simulation Methods  General Features Laboratory experiment Molecular simulation Theory Model Theory + model Theory NC STATE Simulation Methods  General Features • Uses : Industrial applications: Design new products: site specific drugs, new polymers, inhibitors or initiators for crystal growth, solvents for paints, CFC replacements, catalysts, etc. Optimization of existing processes: chemical and physical data for process simulators • The cost of experiments in the laboratory is too high in $ and time to cover more than a fraction of the possible studies. For example, for VLE: Cost of 1 state point ( T for pure; T, x for binary): ~ $3,000 (2 days) Number of commercially important pure substances: ~ 1,000 Number of commercially important binary mixtures: ~ 500,000 Number of commercially important ternary mixtures: ~ 170,000,000 Cost for VLE for all pure substances (10 pts/compound): ~ $30 million...
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This note was uploaded on 08/01/2008 for the course CHEM 596M taught by Professor Franzen during the Spring '08 term at N.C. State.
 Spring '08
 FRANZEN
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