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--- rwp_jumps_continue_after_convergence_etc [2017/02/06 15:30] – johnsoevans
+++ rwp_jumps_continue_after_convergence_etc [2025/09/19 15:18] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
+====== Rwp Jumps, Continue After Convergence, etc ======
+For a well behaved refinement you should normally find that the R-factor that you get when you restart a refinement is identical to the R-factor from the previous convergence.  If this is not the case it normally means there is an error in your input file.
+The most common cause is using the "@" symbol in a multi-data set refinement for a parameter that feeds into multiple data sets.  For example if you have a str that is present in two data sets and write "beq @ 1.37" the temperature factor for that site gets assigned a different parameter name for each data set and two separate values are refined.  Only one value gets stored in the .inp file so your refinement will restart from a different place each time.  The easiest way to spot this is to count the number of parameters you think you're refining with the number Topas reports.
+A second cause is when you have a user defined prm in the input file that refines to a sufficiently small value that it gets rounded in the input file to 0.000000.  One way round this is to just scale the prm by e.g. *10^3 or *10^6 in the equations where it is used.
+If you start a refinement with unit cells a long way from correct values (e.g. 4.65 A when it should be 4.50 A) then the Rwp you get on convergence may not be identical to the value you get when you re-run the file.  In some cases the first Rwp can actually be lower than the value you get subsequently.  This happens as there are a number of quantities that topas only calculates at the start of a refinement.  For example, atomic scattering factors are 2-theta dependent and only calculated when a refinement is started.  if peaks move a lot then their values will be slightly incorrect at convergence.  In a normal Rietveld refinement these effects are minimal.  It is, however, best to run a refinement a couple of times to eliminate these issues. Similarly, peak shapes are also only calculated once and saved in the peaks buffer if they are not flagged to refine; the peaks might need recalculating if peak positions move significantly.  The same occurs for some other aberrations.
+If this is an issue, then one work around is to change your input files to automatically do two convergences rather than one.  In topas v6 this can be done with:
+<code topas>                num_runs 2
+                out_file = Concat(String(INP_File), ".INP"); </code>