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anisotropic_temperature_factors [2009/08/14 15:16]
johnsoevans
anisotropic_temperature_factors [2009/08/27 17:52]
johnsoevans
Line 1: Line 1:
 ===== Anisotropic Temperature Factors ===== ===== Anisotropic Temperature Factors =====
-This is a page that could contain information on adp's in topas, how to create them, what to watch out for and how to stop them being forced to be positive definite.+To refine anisotropically all you need to do is delete "beq @ 0.23" from the end of the site line and type "​adp"​ instead. After one cycle of refinement this line gets replaced by the correct adp macro. In TA all sites are forced to be positive definite ​by default. ​ If you'd rather let adps go negative then think about why (my preference --- //​[[john.evans@durham.ac.uk|John Evans]] 2009/08/27 17:44//) then try adding the macro below: 
 + 
 +<code topas> ​     macro adp_no_limits 
 +
 + move_to u11 min = Val - .05; max = Val + .05; 
 + move_to u22 min = Val - .05; max = Val + .05; 
 + move_to u33 min = Val - .05; max = Val + .05; 
 + move_to u12 min = Val - .05; max = Val + .05; 
 + move_to u13 min = Val - .05; max = Val + .05; 
 + move_to u23 min = Val - .05; max = Val + .05; 
 +}</​code>​ 
 + 
 +Be careful in e.g. multihistogram refinements. ​ Here you can't just use the @ symbol for uij parameter names or they'​ll be different for each histogram. ​ It's always sensible to double check that symmetry restrictions on sites are correct. ​ Try table 8.3.1.1 in International Tables or the table on P104 in Terry Willis'​ text "​Thermal vibrations in crystallography"​.

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