title: Efficient algorithms for semiclassical instanton calculations based on discretized path integrals.
abstract: Path integral instanton method is a promising way to calculate the tunneling splitting of energies for degenerated two state systems. In order to calculate the tunneling splitting, we need to take the zero temperature limit, or the limit of infinite imaginary time duration. In the method developed by Richardson and Althorpe [J. Chem. Phys. 134, 054109 (2011)], the limit is simply replaced by the sufficiently long imaginary time. In the present study, we have developed a new formula of the tunneling splitting based on the discretized path integrals to take the limit analytically. We have applied our new formula to model systems, and found that this approach can significantly reduce the computational cost and gain the numerical accuracy. We then developed the method combined with the electronic structure calculations to obtain the accurate interatomic potential on the fly. We present an application of our ab initio instanton method to the ammonia umbrella flip motion.
authors.affiliation: Institute for Molecular Science, National Institute of Natural Science, 38 Nishigonaka, Myodaiji, Okazaki 222-8585, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Kawatsu
authors.affiliation: School of Mathematics and Physics, Kanazawa University, Kanazawa 920-1192, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Miura
mesh_terms: D000465:Algorithms; D000641:Ammonia / Q000737:chemistry; D003198:Computer Simulation; D008962:Models, Theoretical; D011108:Polymers / Q000737:chemistry*; D011789:Quantum Theory; D013696:Temperature
chemical_list: D011108:Polymers; D000641:Ammonia