Path integral methods for accurate simulation of condensed phase reactions

Simulating a realistic condensed phase reaction (e.g., charge transfer in solution) is a notoriously demanding task. These reactions often involve thousands of strongly coupled atoms. This coupling is complex and extremely non-trivial. Additionally, despite the rapid movement of the atoms themselves, these reactions are usually very slow. A vast majority of chemistry and biology takes place in condensed environments. A method that can accurately simulate these reactions would be invaluable. To that end, we focus on improving the efficiency of a pair of preexisting path integral methods. The first method we discuss treats the entire problem quantum mechanically. While extremely accurate, the computational cost of quantum simulations grows exponentially with the size of the system. To help prevent this, we use an efficient spatial grid as the starting point for an iterative Monte Carlo calculation. Although good methods can mitigate exponential cost, they are still limited to simulations containing only a few atoms. The second method uses a quantum-classical approximation. In these approximations, the majority of the system is simulated using (cheep) classical methods; the (expensive) quantum calculations are reserved for the excessively quantum portions of the system, which tend to be small. The quantum-classical path integral (QCPI) approach handles the interaction between the quantum and classical portions of the system rigorously. By only reducing part of the total system, this QCPI approach introduces nonlocal temporal effects into the simulation. This nonlocality can only be treated by standard iterative-QCPI algorithms, if the coupling between the quantum and classical portions is weak or the simulation time is short. We introduce a scheme that can reduce the effective span of the temporal nonlocality. We employ our new accelerated-QCPI approach to perform an exceedingly accurate simulation of the ferrocene-ferrocenium charge transfer reaction in liquid hexane.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2016

Author dc:creator

• Walters, Peter Lawton

Contributors dc:contributor

• Makri, Nancy
• Hirata, So
• Gruebele, Martin
• Heath, Michael

• Quantum Dynamics
• Path Integral
• Charge Transfer

Statement dc:rights

• Copyright 2016 Peter L. Walters

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/90579

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F90579