TERRIG, a computer program for analysing thermal ellipsoids and rigid-body motions

A program written in Fortran IV for the analysis of thermal ellipsoids and rigid-body motions is reported. The program calculates the thermal vibration ellipsoids of the atoms and performs the rigid-body motion calculations according to the TL method. The validity of the rigid-body assumption is checked by employing the thermal ellipsoid size, shape and orientation criteria of Burns, Ferrier & McMullan [Acta Cryst. (1967), 22, 623-629]. The present program may prove useful in cases where the number of independent thermal parameters of the atom is insufficient to enable the unambiguous determination of the 20 TLS parameters.