Equation of state, compressibility, and vibrational properties of brucite over wide pressure and temperature ranges: Atomistic computer simulations with the modified ClayFF classical force field

Minerals. 2023. Vol. 13. No. 3. Article 408.

Tararushkin E., Pisarev V., Kalinichev A. G.

The behavior of brucite over wide ranges of temperatures and pressures is of great interest
for fundamental geochemistry and geophysics. Brucite layers and their octahedral Mg(OH)6 structural
units constitute an important structural part of layered dense magnesium hydrous silicates
(DMHS), which play a major role in mineral equilibria controlling water balance in the subduction
zones of the upper mantle. The ClayFF force field was originally developed for atomistic computer
simulations of clays and other layered minerals and their hydrated interfaces. The crystallographic
parameters of brucite at 25 C and 1 bar were used, among several others, to develop the original
ClayFF parametrization. Its new recent modification, ClayFF-MOH, can more accurately account for
the bending of Mg–O–H angles in the brucite structure, and it was used here to test the applicability
of this simple classical model over very wide ranges of temperature and pressure well beyond the
range of its original implementation (up to 600 C and 15 GPa). The pressure and temperature
dependencies of brucite crystallographic parameters, the compressibility of the crystal lattice, the
coefficients of thermal expansion, and the vibrational spectra were calculated in a series of classical
molecular dynamics simulations using the ClayFF-MOH model and compared with a diverse set
of available experimental data, including X-ray diffractometry, neutron scattering, IR and Raman
spectroscopy. These new results demonstrated that ClayFF-MOH, as simple and approximate as it is,
can be quite accurate in predicting many mineral properties at subduction zone conditions, which
greatly expands the area of its applicability.

Keywords: structural properties, High pressures, atomistic simulations, Vibrational spectra, elastic properties, high temperatures, brucite

Publication based on the results of: New technologies of supercomputer modeling in material science (2023)