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Author
Title Methods for calculating chemical properties in the condensed phase
URL
Publication Date
Date Accessioned
Discipline/Department Chemistry and Biochemistry
University/Publisher University of Texas – Austin
Abstract With advancements in computer technology and processing power, the ability to examine chemical systems using theory continues to be more practicable. Using ab initio methods, such as density functional theory, we are now able to routinely simulate hundreds of atoms. This system size allows us to directly simulate surfaces and nano-materials that are industrially relevant. With the expansion of accessible systems comes the opportunity to develop new computational methods to extract their chemical properties. Of particular interest is bridging the time scale gap between simulation and experiment. The evolution of a system chemical in time can be directly simulated using classical dynamics, however, molecules vibrate on the order of femtoseconds and interesting transitions tend to happen on much longer time scales: milliseconds to seconds. In condensed phase chemical systems these interesting transitions are hindered by energy barriers so state to state dynamics are dominated by rare evens. Luckily, rare event transitions tend to happen through mountain passes in the potential energy landscape. Within harmonic transition state theory, the transition states between minima can be characterized by saddle points. Finding saddle points is a challenging problem which has not been satisfactorily solved; nevertheless, there are algorithms currently being used despite their deficiency. In particular, my work strives to improve the efficiency and stability of the nudged elastic band method and compare its performance to similar algorithms on a variety of test systems. In addition, I present a method to predict how energy-based chemical properties change with respect to the chemical composition of the system. This is achieved by taking a derivative of the property with respect to the atomic numbers of the atoms present in the system. The accuracy and predictive quality of these derivatives are assessed for both model and industrially relevant systems. With this information, we can follow these derivatives to optimize a desired property in the space of chemical composition. This method is a step toward using theory to rationally design compounds with desirable properties.
Subjects/Keywords Transition state finding; Nudged elastic band; Alchemical derivatives; Rational compound design; Hydrogen diffusion
Contributors Henkelman, Graeme (advisor); Mullins, C. B. (committee member); Rossky, Peter J. (committee member); Vanden Bout, David A. (committee member); Hwang, Gyeong S. (committee member)
Language en
Country of Publication us
Record ID handle:2152/ETD-UT-2010-12-2179
Repository texas
Date Retrieved
Date Indexed 2018-10-22
Note [] text; [department] Chemistry and Biochemistry;

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…Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . Nudged Elastic Band Method . . . . . . . . . . . . . . . . . Convergence Objectives . . . . . . . . . . . . . . . . . . . . Optimization Methods . . . . . . . . . . . . . . . . . . . . . 2.5.1…

NUDGED ELASTIC BAND: A force based optimization method which uses the previous direction moved and the current force to chose a “better” direction for the next optimization step. CONJUGATE GRADIENTS: A method to solve the quantum mechanical electronic…

elastic band. A variation on the NEB where part of the perpendicular spring force is kept to speed up optimization of the MEP. DOUBLY NUDGED ELASTIC BAND: An optimization method based on dynamics with a variable time step and where most of the velocity…

Nudged elastic band. A method for finding the saddle point and subsequent SD path between two adjacent minima on a PES where forces perpendicular to the path are minimized and the images are evenly spaced by tangental acting spring forces. NUDGED ELASTIC

…surface reactions more timely, the effect of optimizer choice and implementation is studied for two-ended saddle point search methods: the nudged elastic band method, the double-nudged elastic band method, the string method, and the new string method. In…

…obtain kinetic data on large systems with direct application to experiments. Here we use an optimized nudged elastic band method to study the 3 diffusion of oxygen vacancies and the hydrogen from adsorbed H2 O on a rutile TiO2 (110) surface…

…computational effort. This paper is structured in the following way. In Sec. 2.3, the nudged elastic band (NEB) method [3, 4, 5], is summarized. In Sec. 2.4 we state our objectives and convergence criteria for finding MEPs. In Sec. 2.5 we…

…x28;111). 2.3 Nudged Elastic Band Method The NEB is a method to find a MEP between a pair of stable states [3]. In the context of reaction rates, this pair has an initial and a final state, both of which are local minima on the potential…

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