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llh2010至尊木蟲 (著名寫手)
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[求助]
ATAT中g(shù)ensqs工具如何改變?nèi)〈鷿舛?
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| 請問各位高手們,使用ATAT軟件包的gensqs工具產(chǎn)生sqs結(jié)構(gòu)時,如何改變?nèi)〈臐舛?例如對于一個bcc結(jié)構(gòu),體心上的一種原子不變,而想讓立方體八個頂點上的另一種原子有一個或幾個被其它原子取代,請問應(yīng)該如何寫lat.in和conc.in文件。 |
學(xué)習(xí) | VASP | 我的分享 |

銀蟲 (小有名氣)
銀蟲 (小有名氣)
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我看到過一個人寫的ATAT產(chǎn)生SQS的筆記,貼在這里,你可以看看: SQS “Tutorial” Amy Bengtson 1 June 2007 Here are my notes on setting up SQS (with many thanks from Yueh-Lin for teaching me). Setting up the most random SQS cells can be subtle, and my notes aren’t perfect, so please make sure you double check everything here. I make special note of the files you may want to double check with Dane. For more explanations, please see the atat manual (section 6.1.8): http://www.its.caltech.edu/~avdw/atat/ http://www.its.caltech.edu/~avdw/atat/manual.pdf I am using CoFe as an example since it is an SQS structure I have set up in the past. In order to get sqs structure for 50% Fe in BCC CoFe: 1. Create a lat.in file. This is the structure from which you want to get the disorded structure. lat.in is of this format: 2.810643 0.000000 0.000000 0.000000 2.810643 0.000000 0.000000 0.000000 2.810643 0.500000 0.500000 0.500000 0.500000 -0.500000 0.500000 0.500000 0.500000 -0.500000 0.000000 0.000000 0.000000 Co,Fe This lat.in is for primitive BCC with one atom. If your primitive cell has more than 1 atom, then continue to list all atomic positions after 0.000000 0.000000 0.000000 Co,Fe. 2. Make conc.in. This tells ATAT what concentration you want to create. conc.in is of the same format as lat.in, only with all atomic positions listed. 2.810643 0.000000 0.000000 0.000000 2.810643 0.000000 0.000000 0.000000 2.810643 -1.000000 0.000000 0.000000 0.000000 0.000000 1.000000 0.000000 1.000000 0.000000 -1.000000 1.000000 1.000000 Fe -0.500000 0.500000 0.500000 Co 3. Now create the clusters by using this command: corrdump -l lat.in -2=maxradius -clus The maxradius is the length of the longest pair desired. A reasonable starting guess is: -2=3 4. Find the correlation of the clusters you created in step 3. Here, maxradius should be the same number as in 3. corrdump -noe -2=maxradius -rnd -s=conc.in > tcorr.out 5. Generate the sqs structure (disorded structures) using this command: gensqs -n=Natoms > sqs.out Where Natoms = the size of the cell you want to create. sqs.out will contain all of the sqs structures, there may be more than 1! The structures will be in the formation of str.out (like conc.in – some conversions will be needed to make them into POSCARs – see step *). 6. In many cases you will find you have many structures in sqs.out. The problem is how to choose which structures to run. You can do two things: a. Redo everything above with a larger maxradius – this will give more correlations to match. Or you can add another radius to match: corrdump -l lat.in -2=maxradius -3=another_radius –clus corrdump -noe -2=maxradius -3=another_radius -rnd -s=conc.in > tcorr.out The “-2” matches pairs, the “-3” matches triplets. b. Rank the sqs structures that you have in sqs.out to find the “most random” structures. To do this: i. Find the correlation on the sqs structures in sqs.out: corrdump -noe -2=LargerRadius -s=sqs.out > tcorr_final.out You want LargerRadius to be larger than maxradius because you are trying find the correlations beyond the original correlation given in tcorr.out. Usually you want to rank based on the first 3 pairs. The columns in tcorr_final.out are: [point correlation] [1st pair] [2nd pair] [3rd pair] [4th pair] … If you don’t have at least 4 columns in your tcorr_final.out, then you need to increase LargerRadius until you have at least 4 columns. Each row corresponds to an sqs structure in sqs.out ii. Find the target correlation out to the LargerRadius corrdump -noe -2= LargerRadius -rnd -s=sqs.out > tcorr_finalRND.out iii. Open tcorr_final.out in excel and rank the structures based on most random. 7. Once you have found which structures from sqs.out you are going to use, split them up and make each structure into its own str.out file. 8. Create a vasp.wrap file that gives the VASP input information. Here is an example: [INCAR] SYSTEM = CoFe ENCUT=455 ISPIND = 2 #makes spin-polarized calc. possible ISPIN = 2 #does spin-polarized calc. MAGMOM= 5 5 5 5 5 5 5 5 ISTART = 0 INIWAV = 1 NSW = 191 IBRION = 2 ISIF = 3 ISMEAR = 1 SIGMA = 0.2 PREC = Accurate LWAVE = .FALSE. KPPRA = 17576 KSCHEME=Monkorst-Pack DOGGA SUBATOM = s/Co/Co/g SUBATOM = s/Fe/Fe_pv/g 9. In the directory with sqs.out, create the VASP input files using this command: runstruct_vasp -nr 10. Run as you normally do. If you make a mistake and need to start over, remove all of these files: rm clusters.out corrdump.log gensqs_0_1.stat sqscell.out sqs* sym.out tcorr.out Important!!! These are the files you should double check with Dane to make sure they were set up correctly. o lat.in o conc,in o tcorr.out o rms ranking (show the Excel sheet where you rank tcorr_final.out) o And confirm that maxradius is a reasonable value. |
銀蟲 (小有名氣)

至尊木蟲 (著名寫手)

至尊木蟲 (著名寫手)
|
周期性結(jié)構(gòu)中八個頂角是等價的,在隨機排布中一個單胞中的八個頂角可能排不同的原子。隨機排布的晶體很多情況下只具有短程有序。 你說的方法我也看到其他人做過,這種方法計算出來的結(jié)果不是很準(zhǔn),原因是這種方法建出來的超胞具有周期性,雖然在一個超胞中是可以隨機取代,但是這個超胞之外的其它超胞就都和它一樣了。而實際情況是所有的超胞都是隨機取代的,和所建的超胞可能相同,也可能不相同。為了克服這個問題,往往需要建很大的超胞,以便達到統(tǒng)計效果,但是問題又來了,機器可能算不動這么大的超胞。 |

銀蟲 (小有名氣)
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看來樓主可能不是用超晶胞方法材料計算方向的。SQS是基于超晶胞方法,用相對較小的晶胞去模擬無序情況,這要求SQS超胞內(nèi)各個原子的周圍環(huán)境‘盡可能’和無序時相近,而且誤差可以衡量。 超晶胞方法進行晶體學(xué)計算中,周期性是必須的,而且如果你用的超胞能夠模擬無序情況了,這個超胞之外的和它等價的那些自然也可以模擬無序。 超晶胞方法模擬不同濃度時是有限制的,比如2%濃度,你只能建一個50個原子的胞,取代其中一個原子,進行模擬,你不能取代半個原子。對于這個限制VCA 和CPA模擬無序就有優(yōu)勢了,濃度可以隨意,不過VCA和CPA都不能進行原子位置的弛豫,有時候這是很大的劣勢。 |
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