self-consistent approach to describe unit-cell-parameter and volume variations with pressure and temperature

A method for the self-consistent description of the large variations of unit-cellparameters of crystals with pressure and temperature is presented. It employslinearized versions of equations of state (EoSs) together with constraints toensure internal consistency. The use of polynomial functions to describe thevariation of the unit-cell angles in monoclinic and triclinic crystals is comparedwith the method of deriving them from linearized EoSs for d spacings. Themethods have been implemented in the CrysFML Fortran subroutine library.The unit-cell parameters and the compressibility and thermal expansion tensorsof crystals can be calculated from the linearized EoSs in an internally consistentmanner in a new utility in the EosFit7c program, which is available as freewareat http://www.rossangel.net.