We develop a free energy density to model a structural first-order phase transformation from a high-temperature cubic phase to a low-temperature tetragonal phase. The free energy density models the softening of the elastic modulus controlling the low-energy path from the cubic to the tetragonal lattice, the loss of stability of the tetragonal phase at high temperatures and the loss of stability...

We determine the relative thermodynamic stability of competing homogeneously and inhomogeneously ordered ferroelectric phases of PbTiO3 using its free-energy landscape, obtained from constrained-polarization moleculardynamics simulations with a first-principles effective Hamiltonian and thermodynamic integration. While we find that the tetragonal structure is thermodynamically most stable at te...

Garnet-type Li7La3Zr2O12 (LLZO) is a solid electrolyte material with a low-conductivity tetragonal and a high-conductivity cubic phase. Using density-functional theory and variable cell shape molecular dynamics simulations, we show that the tetragonal phase stability is dependent on a simultaneous ordering of the Li ions on the Li sublattice and a volume-preserving tetragonal distortion that re...

We carry out first-principles density-functional calculations of the antiferrodistortive ~AFD! and ferroelectric ~FE! soft-mode instabilities in tetragonal SrTiO3, with the structural degrees of freedom treated in a classical, zero-temperature framework. In particular, we use frozen-phonon calculations to make a careful study of the anisotropy of the AFD and FE mode frequencies in the tetragona...

An orthorhombic actin crystal (space group P2(1)2(1)2(1), unit-cell parameters a = 101.6, b = 103.0, c = 127.0 angstroms) was converted into a partially hemihedrally twinned tetragonal crystal (space group P4(3), unit-cell parameters a = b = 101.5, c = 104.2 angstroms) by induced condensation. This condensation (decrease in the c axis) was caused by the flash-freezing of the crystal, with 30% P...