[RMCProfile-users] Problems about RMC result

Tue Aug 4 08:25:52 BST 2015

Dear Huiyang,

Thanks for getting in touch and sorry to hear you've been having some problems. Hopefully I can help!

(1) This may be because there is something is stopping (most of) the atom moves from being accepted, and can sometimes happen when a constraint is applied too heavily, when the maximum move size is set too high or indeed if there is something wrong with the data and no moves can be found that improve the fit.

(2) Minimum distances: You want to set these to a value which you don't want a pair of atoms getting closer than. You can be guided somewhat by your PDF here because you know that you can't have any pairs closer together than the edge of your first peak. 

Maximum moves: your values sound reasonable, personally I usually use between 0.02 and 0.05 (larger maximum moves increase the chances of lots of moves getting rejected).

Time limit: this may be the root of your problem - the times here are very short, so there simply hasn't been time for the atoms to move much. I would try letting the refinement run for several hours at least to see what progress is made.

(3) The weight values tell the program how much that dataset influences the overall fit - a smaller number means a heavier weighting. I assume that there is a default value which is used if you don't include the keyword, but I must admit I don't know what it is! I'd recommend adding this keyword and giving a value of 0.01-0.03 or thereabouts to start with.

Hope this is useful, please get in touch again with any further questions!

Best wishes,
Helen

-----Original Message-----
From: rmcprofile-users [mailto:rmcprofile-users-bounces at rmcprofile.org] On Behalf Of FHY
Sent: 01 August 2015 10:21
To: rmcprofile-users at rmcprofile.org
Subject: [RMCProfile-users] Problems about RMC result

Dear experts

I'm trying to perform a rmc refinement with x-ray data, but the result seems to be not good.so I really need some help.

(1)

After running my rmcprofile, the output <.cfg> shows few accepted steps, I regard it as atom positions don't change a lot, so I tried several different initial configurations and changed atom numbers from 1,000 to 10,000, it still doesn't work.so I just can't find out the solution.

(2)

I changed values in <.dat> file since I'm not sure my minimum distances, maximum moves, time limits are set to be reasonable.

Here is how I set these values

Minimum distances  a little bit less than the sum of radius between two atoms

Maximum moves  I tried 0.01 to 1

Time limits  I tried 1 / 5 /10 min

Are these values reasonable enough?

(3)

I don't know how to set the WEIGHT values of XRAY_RECIPROCAL_SPACE_DATA and NEUTRON_REAL_SPACE_DATA so I didn't write it in my <.dat>file, I don't know whether it's okay ?

I'll be very grateful if you could give me some precious advice

Best regards,

Huiyang Fan

sasorifan at 126.com <mailto:sasorifan at 126.com> 

University of Science and Technology Beijing

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