# A webtool for calculating compressibilities & thermal expansion

Sat, Jan 31, 2015This paper describes PASCal, a simple webtool designed to calculate the principal thermal expansivities or compressibilities of a system from lattice parameters. For low symmetry crystals, the arbitrary choice of unit cell means that if you only look at the cell lengths, it is possible to miss interesting features in the (thermo)mechanical behaviour of a crystal, for example negative thermal expansion or negative compressibilities. PASCal is designed to be an easy method for calculating the principal strain values that give the complete description of these systems. The paper includes three case-studies where re-analysis using PASCal revealed some extra information about the response of the crystals to changing pressure or temperature.

*Figure: By choosing different unit cells, the response along the unit cell axes can appear to be very different - only the principal axes give the true response.*

### Paper

PASCal: a principal axis strain calculator for thermal expansion and compressibility determination

M J Cliffe and A L Goodwin

*J Appl Cryst*, **45**, 1321-1329 (2012).