title: Nuclear dynamics in the metastable phase of the solid acid caesium hydrogen sulfate.
abstract: High-resolution spectroscopic measurements using thermal and epithermal neutrons and first-principles calculations within the framework of density-functional theory are used to investigate the nuclear dynamics of light and heavy species in the metastable phase of caesium hydrogen sulfate. Within the generalised-gradient approximation, extensive calculations show that both 'standard' and 'hard' formulations of the Perdew-Burke-Ernzerhof functional supplemented by Tkatchenko-Scheffler dispersion corrections provide an excellent description of the known structure, underlying vibrational density of states, and nuclear momentum distributions measured at 10 and 300 K. Encouraged by the agreement between experiment and computational predictions, we provide a quantitative appraisal of the quantum contributions to nuclear motions in this solid acid. From this analysis, we find that only the heavier caesium atoms reach the classical limit at room temperature. Contrary to naïve expectation, sulfur exhibits a more pronounced quantum character relative to classical predictions than the lighter oxygen atom. We interpret this hitherto unexplored nuclear quantum effect as arising from the tighter binding environment of this species in this technologically relevant material.
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK. felix.fernandez-alonso@stfc.ac.uk and School of Science and Technology, Nottingham Trent University, Clifton Campus, Nottingham, NG11 8NS, UK.
authors.forename: Maciej
authors.initials: M
authors.lastname: Krzystyniak
authors.affiliation: Faculty of Physics, Adam Mickiewicz University, Umultowska St. 85, 61-614 Poznan, Poland and Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, 141980, Dubna, Russian Federation.
authors.forename: Kacper
authors.initials: K
authors.lastname: Drużbicki
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK. felix.fernandez-alonso@stfc.ac.uk and Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK.
authors.forename: Felix
authors.initials: F
authors.lastname: Fernandez-Alonso