@article{zhang_cheng_kolesnikov_bernholc_lu_ramirez-cuesta_2021, title={Study of Anharmonicity in Zirconium Hydrides Using Inelastic Neutron Scattering and Ab-Initio Computer Modeling}, volume={9}, ISSN={["2304-6740"]}, url={https://doi.org/10.3390/inorganics9050029}, DOI={10.3390/inorganics9050029}, abstractNote={The anharmonic phonon behavior in zirconium hydrides and deuterides, including ϵ-ZrH2, γ-ZrH, and γ-ZrD, has been investigated from aspects of inelastic neutron scattering (INS) and lattice dynamics calculations within the framework of density functional theory (DFT). The harmonic model failed to reproduce the spectral features observed in the experimental data, indicating the existence of anharmonicity in those materials and the necessity of further explanations. Here, we present a detailed study on the anharmonicity in zirconium hydrides/deuterides by exploring the 2D potential energy surface of hydrogen/deuterium atoms and solving the corresponding 2D single-particle Schrödinger equation to obtain the eigenfrequencies, which are then convoluted with the instrument resolution. The convoluted INS spectra qualitatively describe the anharmonic peaks in the experimental INS spectra and demonstrate that the anharmonicity originates from the deviations of hydrogen potentials from quadratic behavior in certain directions; the effects are apparent for the higher-order excited vibrational states, but small for the ground and first excited states.}, number={5}, journal={INORGANICS}, author={Zhang, Jiayong and Cheng, Yongqiang and Kolesnikov, Alexander I. and Bernholc, Jerry and Lu, Wenchang and Ramirez-Cuesta, Anibal J.}, year={2021}, month={May} }
 @article{pandey_zhang_cheng_daemen_ramirez-cuesta_2019, title={Theoretical Study of Alkali-Metal Hydrides at High Pressures: A Case of NaH Supported by Inelastic Neutron Scattering (INS) Experiments at 1 and 2 GPa}, volume={123}, ISSN={["1520-5215"]}, DOI={10.1021/acs.jpca.9b07971}, abstractNote={Pressure-induced effects in alkali hydrides are investigated using a plane-wave density functional theory method. For the first time, we have measured the inelastic neutrons scattering (INS) spectra of NaH at pressures 1 GPa and 2 GPa and used it to validate INS simulated from the first-principles calculations using both local density approximation (LDA) and the generalized gradient approximation (GGA). We found that LDA describes lattice dynamics better compared to the GGA. Thermodynamic properties such as lattice parameters, bulk modulus, and their derivatives are calculated using full lattice dynamics theory within the quasi-harmonic approximation (QHA) for all alkali hydrides. Anharmonic effects are investigated for NaH from the molecular dynamics trajectories and are negligible at given temperature and pressures. We have shown that the phase-change pressures obtained from the equal Gibbs free energy conditions for two phases compare well with the available experimental data and is the accurate phase-change criterion. This study corroborates INS as an important complementary tool in benchmarking first-principles calculations.}, number={46}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, author={Pandey, Anup and Zhang, Jiayong and Cheng, Yongqiang and Daemen, Luke and Ramirez-Cuesta, Anibal J.}, year={2019}, month={Nov}, pages={10079–10085} }