jz501985w_si_001.pdf (901.6 kB)
Periodic MP2, RPA, and Boundary Condition Assessment of Hydrogen Ordering in Ice XV
journal contribution
posted on 2015-12-17, 06:08 authored by Mauro Del Ben, Joost VandeVondele, Ben SlaterIce
XV is the hydrogen-ordered form of the ice VI phase whose structure
was predicted to be Cc and ferroelectric using periodic
DFT approaches. However, neutron diffraction and Raman spectroscopy
data show the structure to have P1̅ symmetry
and to be antiferroelectric. Recent work using fragment-based MP2 and CCSD(T) approaches predicts the experimental
structure as the ground state. We have reconsidered this problem using
fully periodic MP2 and RPA approaches and find that the ferroelectric Cc structure is the lowest energy configuration. However,
ubiquitously employed tinfoil boundary conditions stabilize polar
structures. We suggest that ferroelectric Cc crystals
can grow within a paraelectric ice VI matrix but may become unstable
once a fraction of the matrix has become hydrogen-ordered. The reduction
in dielectric constant causes P1̅ and other
structures with small polarization to become favored, providing a
possible resolution between observation and theoretical predictions.