[RMCProfile-users] Atoms in starting configuration for RMCProfile

[helen.playford at stfc.ac.uk]

Hi Romain,

A particular command in data2config should do most of what you need. For example, say if my GSAS-obtained structure looks like this:

Atom	x	y	z	occupancy

Zr	0	0	0	0.5	
Y	0	0	0	0.5
O	0.25	0.25	0.25	0.875

The Y and Zr will share a site, and the O site has 1.25% vacancies. The command:

data2config -rmc6f -replace[Zr 0.5 Y:O 0.125 Va] -order[Y Zr O Va] y2zr2o7.tbl

should produce a configuration file with the Zr and Y shared across a single site, and some of the oxygen positions occupied by vacancies.

At present, if you have, for example, 2 oxygen sites that are distinct crystallographically, these will be lumped in to one atom type by data2config when it builds the RMC configuration. If you need this functionality I can talk you through a workaround but it is a bit tedious! 

The next incremental update of RMCProfile, which should be out soon, will have a version of data2config that will automatically detect structures like this, and hopefully produce appropriate configurations. 

Best wishes,
Helen


-----Original Message-----
From: rmcprofile-users [mailto:rmcprofile-users-bounces at rmcprofile.org] On Behalf Of Romain Sibille
Sent: 21 July 2016 16:58
To: rmcprofile-users at rmcprofile.org
Subject: [RMCProfile-users] Atoms in starting configuration for RMCProfile

Dear all,

I am investigating neutron PDF data using RMCProfile.  It's a crystalline material with some sort of disorder.

I went through the first steps: generate appropriate output files from GSAS, make data2config run, and RMCprofile itself works as well with my files.

I don't understand how and at which step of the procedure one can choose to keep distinct types of atoms in the supercell for atoms which were on distinct Wyckoff positions in the original crystallographic unit-cell.  
In other words: I have a metal M and two O positions and one oxygen vacancy, and I would like to keep the distinction between the O atoms from the two positions and introduce non-scattering 'Va' atoms for the positions for the vacancies (with the goal of, for example, using SWAP between one oxygen site and the vacancy site).

Best wishes,

Romain

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