Rietveld analysis programs RIETAN and PREMOS and special applications

Abstract A FORTRAN program named RIETAN (RIETveld ANalysis) was independently developed in Japan for Rietveld analysis of angle-dispersive X-ray and neutron powder data (Izumi 1985; Izumi 1989). It has since become the heart of a suite of related programs called FAT-RIETAN (Section 13.2). RIETAN was later modified to work with TOF neutron powder data (Izumi et al.1987) measured on the high-resolution powder diffractometer, HRP (Watanabe et al.1987), installed at the KENS pulsed neutron source at the National Laboratory for High Energy Physics (KEK). Since 1983, structures of many metals and inorganic compounds, most of which are superconducting copper oxides and related compounds, have been refined routinely with this program. As well as having many of the ‘usual’ features of other good programs, such as GSAS and DBWS-9006 described in Chapter 1, RIETAN has some special features of interest. Chief among them are (i) a choice of three different least-squares algorithms (Section 13.1.6), (ii) the possibility to change from one algorithm to another under programmatic control to confirm the convergence to a global minimum (Section 13.1.7), and (iii) incremental refinement in which variable parameters in each cycle are changed appropriately during the course of a refinement series (Section 13.1.7). Databases storing crystallographic information and physical quantities of elements are attached to RIET AN (Section 13.1.2). Both linear and non-linear constraints can be accommodated, the latter along with an exterior penalty function method (Section 13.1.5).