Compressive behavior and electronic properties of ammonia ice: a first-principles study. Issue 44 (16th July 2020)

• Record Type: Journal Article
• Authors: Yu, Xueke; Jiang, Xue; Su, Yan; Zhao, Jijun
• Is Part Of: RSC advances. Volume 10:Issue 44(2020)
• Page Start: 26579
• Page End: 26587
• Publication Date: 2020-07-16
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d0ra03248d
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : We performed systematic ab initio calculations to explore the structures and electronic properties of ammonia ice by hydrostatic compression. Abstract : Understanding the compressive behavior of ammonia ice is an enduring topic due to its salient implications in planetology and the origin of life as well as its applications in agriculture and industry. Currently, the most stable crystal structures of ammonia ice with increasing pressure have been determined to be P 21 3, P 21 21 21, Pma 2, Pca 21, P 21 / m and Pnma, respectively. Taking these six crystal structures for consideration, the pressure-induced structural and electronic behavior of ammonia ice was systematically investigated using density functional theory calculations. According to our calculations, the transition from molecular phase P 21 21 21 to ionic phase Pma 2 can be ascribed to the bonds between H atoms and N atoms on adjacent NH3 molecules. Analysis of the Mulliken population and electron density of states implies decreased charge transfer between the N and H atoms and enhanced bonds with increasing pressure. In addition, charge overlap between NH3 molecules was found at high pressure in the molecular phases of ammonia ice, which is also observed between NH2 − and NH4 + groups in ionic phases. With increasing pressure, the band gap of ammonia ice increases rapidly and then decreases gradually, which is a consequence of the subtle competition between the strong coupling in the H 1s and N 2p states and the charge overlap. These simulations help us understand the characteristics of ammonia ice under high pressure and further provide valuable insights into the evolution of planets.