title: Near spectroscopically accurate ab initio potential energy surface for NH4(+) and variational calculations of low-lying vibrational levels.
abstract: A nine-dimensional potential energy surface (PES) for the ammonium cation has been constructed by fitting ∼30 000 AE-CCSD(T)-F12a/cc-pCVTZ-F12 points up to 32 262 cm(-1) (4.0 eV) from the minimum. The fitting using the permutation invariant polynomial-neural network method has high fidelity, with a root-mean-square error of merely 2.34 cm(-1). The low-lying vibrational energy levels of NH4(+) have been determined quantum mechanically using both Jacobi and normal coordinates, and the fundamental frequencies are in excellent agreement with available experimental data.
authors.affiliation: †Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United States.|‡School of Physics, Northwest University, Xi'an, Shaanxi 710069, China.
authors.forename: Huixian
authors.initials: H
authors.lastname: Han
authors.affiliation: †Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United States.
authors.forename: Hongwei
authors.initials: H
authors.lastname: Song
authors.affiliation: §School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400030, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.affiliation: †Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United States.
authors.forename: Hua
authors.initials: H
authors.lastname: Guo