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SUMMARY:DMC-ICE13: ambient and high pressure polymorphs of ice from Diffus
 ion Monte Carlo and Density Functional Theory - Flaviano Della Pia\, Unive
 rsity of Cambridge
DTSTART:20230201T143000Z
DTEND:20230201T150000Z
UID:TALK193642@talks.cam.ac.uk
CONTACT:Lisa Masters
DESCRIPTION:Ice is one of the most important and interesting molecular cry
 stals\, exhibiting a rich and evolving phase diagram. Recent discoveries m
 ean that there are now 20 distinct polymorphs\; a structural diversity tha
 t arises from a delicate interplay of hydrogen bonding and van der Waals d
 ispersion forces. This wealth of structures provides a stern test of elect
 ronic structure theories\, with Density Functional Theory (DFT) often not 
 able to accurately characterise the relative energies of the various ice p
 olymorphs. Thanks to recent advances that enable the accurate and efficien
 t treatment of molecular crystals with Diffusion Monte Carlo (DMC)\, we pr
 esent here the DMC-ICE13 dataset\; a dataset of lattice energies of 13 ice
  polymorphs. This dataset encompasses the full structural complexity found
  in the ambient and high-pressure molecular ice polymorphs\, and when expe
 rimental reference energies are available\, our DMC results deliver sub-ch
 emical accuracy. Using this dataset\, we then perform an extensive benchma
 rk of a broad range of DFT functionals. Our results suggest that a single 
 functional achieving reliable performance for all phases is still missing\
 , and that care is needed in the selection of the most appropriate functio
 nal for the desired application. The insights obtained here may also be re
 levant to liquid water and other hydrogen-bonded and dispersion-bonded mol
 ecular crystals. 
LOCATION:Unilever Lecture Theatre\, Yusuf Hamied Department of Chemistry
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