Abstract
In this work, we consider low-enthalpy polymorphs of ice, predicted previously using a modified basin-hopping algorithm for crystal-structure prediction with the TIP4P empirical potential at three pressures (0, 4 and 8 kbar). We compare and (re)-rank the reported ice polymorphs in order of energetic stability, using high-level quantum-chemical calculations, primarily in the guise of sophisticated Density-Functional Theory (DFT) approaches. In the absence of applied pressure, ice Ih is predicted to be energetically more stable than ice Ic, and TIP4P-predicted results and ranking compare well with the results obtained from DFT calculations. However, perhaps not unexpectedly, the deviation between TIP4P- and DFT-calculated results increases with applied external pressure.
Highlights
The study of water’s properties, regardless of the particular condensed phase thereof, is of paramount practical and technical interest, in addition to constituting a fundamental and formidable scientific challenge [1]
We compare the relative TIP4P lattice enthalpies with those of PBE-D3 and PBE-many-body dispersion (MBD) (Figure 2), at different pressures (0 bar, 4000 bar and 8000 bar); i.e., the enthalpies relative to the lowest-energy structures
At 0 kbar, both PBE-D3- and PBE-MBD-relative enthalpies are well correlated with TIP4P enthalpy, with very limited re-ranking occurring for some higher-enthalpy polymorphs
Summary
The study of water’s properties, regardless of the particular condensed phase thereof, is of paramount practical and technical interest, in addition to constituting a fundamental and formidable scientific challenge [1]. Theoretical and/or molecular-simulation studies can help to explain more insights into the rich behavior of solid (both crystalline and amorphous) water phases, especially for high-pressure ices at the electronic-structure level, where empirical models can often be found wanting (due to the inevitable electron-cloud overlap at high pressures being well outside the electronic experience of near-ambient-condition empirical-model parameterization) [13]. The theoretical pursuit, and leverage, of crystal-structure-prediction (CSP) methods can be used to explore the plausible different crystalline polymorphs, and polytypes, of ice [14]. CSP, done well, can provide de-novo predictions for various crystalline polymorphs of a material from a first-principles approach (either with accurate empirical force-fields or from electronic-structure approaches). DFT and structure prediction; here, we re-rank the ice polymorphs using sophisticated and higher-level higher-level electronic-structure calculations [14]. Some of the polymorph structures are shown in electronic-structure calculations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
