Greetings Alex and ATAT users,
I have tried the provided example, Al-Cu system using maps. However, it does not converge even more than 120 structures are calculated. Is it normal?
maps.log
The internal database of structures extends at least up to 8 atoms/unit cell, see predstr.out
Among structures of known energy, true ground states differ from fitted ground states
New ground states with at most 9 atoms/unit cell predicted , see predstr.out
Concentration range used for ground state checking: [0,1].
Crossvalidation score: 0.0957489
Hi Alex,
I have increased the kppra to 8000. However, it still fails to convergent after calculating 70 clusters. Do you have any further suggestions? Thank you very much.
Regards,
Hui
Maps version 3.23
The internal database of structures extends at least up to 7 atoms/unit cell, see predstr.out
Among structures of known energy, true ground states differ from fitted ground states
New ground states with at most 8 atoms/unit cell predicted , see predstr.out
Concentration range used for ground state checking: [0,1].
Crossvalidation score: 0.108548
Problem getting the right ground states have been discussed in many other posts. Either reduce the composition range to the minimum you need (-c0 and -c1 options) or if the issue is relaxation to another lattice, use robustrelax_vasp (see https://dx.doi.org/10.1038/ncomms8559 ).
I’m working on a cluster expansion for the Al-Cu system using ATAT in the Al-rich regime. After spending a lot of time on learning how to work with ATAT and doing a lot of DFT and CE-fitting using MAPS, I finally ended up with a well working CE (using 46 input structures), obtaining the correct ground states for Al-rich alloys (GP-zones) and getting good values for transition temperatures during simulated annealing MC-simulations.
On my way I have noticed some important points you maybe should take into account when dealing with Al-Cu:
Construction of a reciprocal CE (using the csfit module) improves the convergence of the CE a lot, due to the large mismatch of lattice constants of Al and Cu.
Using the checkrelax command and flagging the severely deformed structures with an error is important, because a lot of structures won’t fit the fcc lattice after relaxation. This is due to the large number of non-fcc based intermetallic phases showing up in the Al-Cu phase diagram.
For me, using the -c1 options of MAPS was helpful, because I’m only interested in the Al-rich part of the phase diagram. By this I didn’t waste too much time with the calculation of unstable phases.
I think these points will be helpful for getting your work done. Feel free to contact me!
I have tried the TiAl system using the following parameters as INCA.
[INCAR]
Encut =500
ISTART = 0
ICHARG = 2
IBRION =2
EDIFF =1E-6
ISMEAR = -1
SIGMA = 0.1
NSW=41
IBRION = 2
ISIF = 3
KPPRA = 8000
DOSTATIC
The parameters are good enough for high precision. However, the result of the fit is very bad. The energy difference of many structures can be more 50%. I attach the fit.out here. Should I exclude all those structures? Would you please help me have a check where the problem is? Thank you very much.
Regards,
Hui
Thank you for your detailed explanations. Indeed, the checkrelax is very useful. But I am still struggling to get a convergent result. Thank you again.
Regards,
Hui
Ti-Al is a typical system where the most stable lattice changes as a function of composition (hcp for Ti-rich, fcc for Al-rich and even bcc around 50%). So, some structures will certainly relax away from the intended lattice.
Possible solutions (use one of them consistently, not a mix!):
limit the composition range with the -c0=… -c1=… options of maps
Use checkrelax to see which structures have relaxed too much and drop them. (touch nn/error)