title: Towards black-box calculations of tunneling splittings obtained from vibrational structure methods based on normal coordinates.
abstract: Multidimensional potential energy surfaces obtained from explicitly correlated coupled-cluster calculations and further corrections for high-order correlation contributions, scalar relativistic effects and core-correlation energy contributions were generated in a fully automated fashion for the double-minimum benchmark systems OH3(+) and NH3. The black-box generation of the potentials is based on normal coordinates, which were used in the underlying multimode expansions of the potentials and the μ-tensor within the Watson operator. Normal coordinates are not the optimal choice for describing double-minimum potentials and the question remains if they can be used for accurate calculations at all. However, their unique definition is an appealing feature, which removes remaining errors in truncated potential expansions arising from different choices of curvilinear coordinate systems. Fully automated calculations are presented, which demonstrate, that the proposed scheme allows for the determination of energy levels and tunneling splittings as a routine application.
authors.affiliation: Institute of Theoretical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Neff
authors.forename: Guntram
authors.initials: G
authors.lastname: Rauhut
mesh_terms: D000465:Algorithms; D000641:Ammonia / Q000737:chemistry*; D003198:Computer Simulation; D008956:Models, Chemical; D009861:Onium Compounds / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D009861:Onium Compounds; C027727:hydronium ion; D000641:Ammonia
keywords: Ammonia; Hydronium ion; Normal coordinates; Tunneling splittings; VCI calculations