Locating Instantons in Calculations of Tunneling Splittings: The Test Case of Malonaldehyde
| Autor: | Stuart C. Althorpe, Marko T. Cvitaš |
|---|---|
| Rok vydání: | 2016 |
| Předmět: |
Physics
Instanton 010304 chemical physics 010402 general chemistry 01 natural sciences Potential energy Action (physics) 0104 chemical sciences Computer Science Applications Orders of magnitude (time) Position (vector) Quantum mechanics 0103 physical sciences Path (graph theory) semiclassical instanton tunneling splittings C++ string handling Physical and Theoretical Chemistry Quantum tunnelling |
| Zdroj: | Journal of chemical theory and computation. 12(2) |
| ISSN: | 1549-9626 |
| Popis: | The recently developed ring-polymer instanton (RPI) method [J. Chem. Phys. 2011, 134, 054109] is an efficient technique for calculating approximate tunneling splittings in high- dimensional molecular systems. The key step is locating the instanton tunneling path at zero temperature. Here, we show that techniques previously designed for locating instantons in finite-temperature rate calculations can be adapted to the RPI method, where they become extremely efficient, reducing the number of potential energy calls by 2 orders of magnitude. We investigate one technique that employs variable time steps to minimize the action integral, and two that employ equally spaced position steps to minimize the abbreviated (i.e., Jacobi) action integral, using respectively the nudged elastic band (NEB) and string methods. We recommend use of the latter because it is parameter-free, but all three methods give comparable efficiency savings. Having located the instanton pathway, we then interpolate the instanton path onto a fine grid of imaginary time points, allowing us to compute the fluctuation prefactor. The crucial modification needed to the original finite-temperature algorithms is to allow the end points of the zero-temperature instanton path to describe overall rotations, which is done using a standard quaternion algorithm. These approaches will allow the RPI Method to be combined effectively with expensive potential energy surfaces or on-the-fly electronic structure methods. |
| Databáze: | OpenAIRE |
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