Inquiry about Element Notation in POSCAR File.

[hszhao.cn@gmail.com]

Dear VASP Community,

I am currently engaged in preparing POSCAR files for a series of calculations using VASP. Through the use of an external tool (interface_master), a POSCAR file was generated with an unconventional notation for specifying elements, as shown below:

Code: Select all

#POSCAR generated by IF_master 
1
43.9602737390538962 -0.0000000000000006 0.0000000000000015 
3.8669746532647458 6.6977965710355809 0.0000000000000001 
11.6009239597942404 -11.1629942850593036 22.1016010804739054 
Ag+ S2- Si 
72 36 84 
Direct
0.3359972411333182 0.8725380263659073 0.8266111345059748
0.4551323086572752 0.5675971321721788 0.6464322781207835
0.5742673761812320 0.2626562379784498 0.4662534217355923
0.3359972411333182 0.8725380263659074 0.4932778011726415
0.4551323086572752 0.5675971321721787 0.3130989447874502
0.5742673761812322 0.2626562379784499 0.1329200884022590
0.3359972411333184 0.8725380263659075 0.1599444678393081
0.4551323086572753 0.5675971321721786 0.9797656114541169
0.5742673761812325 0.2626562379784495 0.7995867550689254
0.3109290784950621 0.8225210794403636 0.6598766757755008
0.4300641460190193 0.5175801852466346 0.4796978193903095
0.5491992135429763 0.2126392910529057 0.2995189630051182
0.3109290784950623 0.8225210794403637 0.3265433424421674
0.4300641460190193 0.5175801852466348 0.1463644860569762
0.5491992135429763 0.2126392910529059 0.9661856296717848
0.3109290784950623 0.8225210794403637 0.9932100091088339
0.4300641460190194 0.5175801852466350 0.8130311527236427
0.5491992135429764 0.2126392910529059 0.6328522963384513
0.2649360325968984 0.4402459511710061 0.7674168313805215
0.3840711001208553 0.1353050569772773 0.5872379749953303
0.5032061676448125 0.8303641627835484 0.4070591186101389
0.2649360325968985 0.4402459511710062 0.4340834980471882
0.3840711001208555 0.1353050569772773 0.2539046416619968
0.5032061676448125 0.8303641627835484 0.0737257852768055
0.2649360325968986 0.4402459511710062 0.1007501647138548
0.3840711001208554 0.1353050569772775 0.9205713083286635
0.5032061676448126 0.8303641627835484 0.7403924519434721
0.3819902870314820 0.2548131546352649 0.7190709789009541
0.5011253545554389 0.9498722604415363 0.5388921225157628
0.6202604220793960 0.6449313662478071 0.3587132661305715
0.3819902870314820 0.2548131546352650 0.3857376455676206
0.5011253545554389 0.9498722604415362 0.2055587891824294
0.6202604220793959 0.6449313662478073 0.0253799327972381
0.3819902870314822 0.2548131546352650 0.0524043122342873
0.5011253545554392 0.9498722604415362 0.8722254558490961
0.6202604220793961 0.6449313662478073 0.6920465994639047
0.2901223772221381 0.7264563967295099 0.7907305526854617
0.4092574447460952 0.4215155025357813 0.6105516963002704
0.5283925122700522 0.1165746083420524 0.4303728399150791
0.2901223772221382 0.7264563967295099 0.4573972193521283
0.4092574447460952 0.4215155025357812 0.2772183629669370
0.5283925122700524 0.1165746083420523 0.0970395065817457
0.2901223772221382 0.7264563967295100 0.1240638860187949
0.4092574447460953 0.4215155025357812 0.9438850296336037
0.5283925122700522 0.1165746083420524 0.7637061732484123
0.3568039424062423 0.9686027090767610 0.6957572575960139
0.4759390099301992 0.6636618148830322 0.5155784012108227
0.5950740774541563 0.3587209206893032 0.3353995448256313
0.3568039424062423 0.9686027090767610 0.3624239242626806
0.4759390099301993 0.6636618148830323 0.1822450678774893
0.5950740774541563 0.3587209206893034 0.0020662114922980
0.3568039424062424 0.9686027090767612 0.0290905909293472
0.4759390099301994 0.6636618148830322 0.8489117345441559
0.5950740774541564 0.3587209206893034 0.6687328781589645
0.3547040677060650 0.4739775972778196 0.8597244234519927
0.4738391352300219 0.1690367030840909 0.6795455670668015
0.5929742027539791 0.8640958088903621 0.4993667106816101
0.3547040677060650 0.4739775972778198 0.5263910901186594
0.4738391352300220 0.1690367030840909 0.3462122337334682
0.5929742027539791 0.8640958088903621 0.1660333773482768
0.3547040677060651 0.4739775972778197 0.1930577567853259
0.4738391352300222 0.1690367030840909 0.0128789004001347
0.5929742027539791 0.8640958088903621 0.8327000440149434
0.2922222519223154 0.2210815085284513 0.6267633868294828
0.4113573194462724 0.9161406143347224 0.4465845304442916
0.5304923869702295 0.6111997201409934 0.2664056740591003
0.2922222519223155 0.2210815085284513 0.2934300534961495
0.4113573194462725 0.9161406143347225 0.1132511971109582
0.5304923869702295 0.6111997201409936 0.9330723407257669
0.2922222519223156 0.2210815085284512 0.9600967201628161
0.4113573194462726 0.9161406143347224 0.7799178637776247
0.5304923869702295 0.6111997201409936 0.5997390073924336
0.3070816114893760 0.5299991456183502 0.6891338852757938
0.4262166790133330 0.2250582514246213 0.5089550288906025
0.5453517465372900 0.9201173572308924 0.3287761725054112
0.3070816114893760 0.5299991456183500 0.3558005519424605
0.4262166790133332 0.2250582514246212 0.1756216955572692
0.5453517465372901 0.9201173572308922 0.9954428391720779
0.3070816114893762 0.5299991456183500 0.0224672186091271
0.4262166790133333 0.2250582514246212 0.8422883622239358
0.5453517465372902 0.9201173572308923 0.6621095058387445
0.3398447081390044 0.1650599601879210 0.7973539250056818
0.4589797756629613 0.8601190659941922 0.6171750686204905
0.5781148431869184 0.5551781718004634 0.4369962122352993
0.3398447081390044 0.1650599601879211 0.4640205916723484
0.4589797756629615 0.8601190659941922 0.2838417352871571
0.5781148431869185 0.5551781718004634 0.1036628789019658
0.3398447081390045 0.1650599601879211 0.1306872583390151
0.4589797756629614 0.8601190659941923 0.9505084019538237
0.5781148431869185 0.5551781718004634 0.7703295455686324
0.2834566510591053 0.8093921447005433 0.8915307398790695
0.4025917185830621 0.5044512505068145 0.7113518834938782
0.5217267861070193 0.1995103563130855 0.5311730271086870
0.2834566510591052 0.8093921447005433 0.5581974065457361
0.4025917185830623 0.5044512505068145 0.3780185501605449
0.5217267861070194 0.1995103563130855 0.1978396937753535
0.2834566510591053 0.8093921447005434 0.2248640732124028
0.4025917185830624 0.5044512505068146 0.0446852168272115
0.5217267861070195 0.1995103563130856 0.8645063604420201
0.3634696685692752 0.8856669611057276 0.5949570704024060
0.4826047360932322 0.5807260669119989 0.4147782140172148
0.6017398036171894 0.2757851727182697 0.2345993576320234
0.3634696685692753 0.8856669611057276 0.2616237370690727
0.4826047360932323 0.5807260669119987 0.0814448806838814
0.6017398036171893 0.2757851727182700 0.9012660242986901
0.3634696685692754 0.8856669611057277 0.9282904037357393
0.4826047360932323 0.5807260669119988 0.7481115473505480
0.6017398036171894 0.2757851727182700 0.5679326909653567
0.0600677357810227 0.1785714285714285 0.1071428571428571
0.1480329444650933 0.1785714285714285 0.1071428571428571
0.2359981531491639 0.1785714285714285 0.1071428571428571
0.0600677357810227 0.6785714285714286 0.1071428571428571
0.1480329444650933 0.6785714285714286 0.1071428571428571
0.2359981531491639 0.6785714285714286 0.1071428571428571
0.0600677357810227 0.2499999999999998 0.2499999999999999
0.1480329444650933 0.2499999999999999 0.2500000000000000
0.2359981531491639 0.2499999999999999 0.2500000000000000
0.0600677357810227 0.7499999999999999 0.2500000000000000
0.1480329444650933 0.7499999999999999 0.2500000000000000
0.2359981531491639 0.7500000000000000 0.2500000000000000
0.0600677357810227 0.3214285714285712 0.3928571428571428
0.1480329444650933 0.3214285714285712 0.3928571428571427
0.2359981531491639 0.3214285714285712 0.3928571428571427
0.0600677357810228 0.8214285714285713 0.3928571428571428
0.1480329444650933 0.8214285714285713 0.3928571428571428
0.2359981531491639 0.8214285714285713 0.3928571428571428
0.0600677357810227 0.3928571428571427 0.5357142857142857
0.1480329444650932 0.3928571428571427 0.5357142857142857
0.2359981531491639 0.3928571428571427 0.5357142857142857
0.0600677357810227 0.8928571428571428 0.5357142857142857
0.1480329444650933 0.8928571428571428 0.5357142857142857
0.2359981531491639 0.8928571428571428 0.5357142857142857
0.0600677357810227 0.4642857142857140 0.6785714285714285
0.1480329444650933 0.4642857142857140 0.6785714285714285
0.2359981531491639 0.4642857142857140 0.6785714285714285
0.0600677357810227 0.9642857142857142 0.6785714285714285
0.1480329444650933 0.9642857142857142 0.6785714285714285
0.2359981531491639 0.9642857142857142 0.6785714285714285
0.0600677357810227 0.0357142857142857 0.8214285714285714
0.1480329444650933 0.0357142857142857 0.8214285714285714
0.2359981531491639 0.0357142857142857 0.8214285714285714
0.0600677357810227 0.5357142857142855 0.8214285714285714
0.1480329444650932 0.5357142857142855 0.8214285714285714
0.2359981531491639 0.5357142857142855 0.8214285714285714
0.0600677357810227 0.1071428571428567 0.9642857142857142
0.1480329444650933 0.1071428571428567 0.9642857142857142
0.2359981531491639 0.1071428571428567 0.9642857142857142
0.0600677357810227 0.6071428571428570 0.9642857142857142
0.1480329444650933 0.6071428571428570 0.9642857142857142
0.2359981531491639 0.6071428571428570 0.9642857142857142
0.0160851314389874 0.2857142857142856 0.0714285714285714
0.1040503401230580 0.2857142857142857 0.0714285714285714
0.1920155488071286 0.2857142857142857 0.0714285714285714
0.0160851314389874 0.7857142857142856 0.0714285714285714
0.1040503401230580 0.7857142857142856 0.0714285714285714
0.1920155488071286 0.7857142857142856 0.0714285714285714
0.0160851314389874 0.3571428571428570 0.2142857142857142
0.1040503401230579 0.3571428571428571 0.2142857142857143
0.1920155488071286 0.3571428571428571 0.2142857142857143
0.0160851314389874 0.8571428571428571 0.2142857142857142
0.1040503401230580 0.8571428571428571 0.2142857142857142
0.1920155488071286 0.8571428571428571 0.2142857142857142
0.0160851314389874 0.4285714285714284 0.3571428571428571
0.1040503401230580 0.4285714285714284 0.3571428571428571
0.1920155488071286 0.4285714285714284 0.3571428571428570
0.0160851314389874 0.9285714285714284 0.3571428571428571
0.1040503401230580 0.9285714285714284 0.3571428571428571
0.1920155488071286 0.9285714285714285 0.3571428571428571
0.0160851314389874 0.9999999999999999 0.5000000000000000
0.1040503401230580 0.9999999999999999 0.5000000000000000
0.1920155488071286 0.9999999999999999 0.5000000000000000
0.0160851314389874 0.4999999999999998 0.5000000000000000
0.1040503401230580 0.4999999999999998 0.5000000000000000
0.1920155488071286 0.4999999999999998 0.4999999999999999
0.0160851314389874 0.0714285714285712 0.6428571428571428
0.1040503401230580 0.0714285714285712 0.6428571428571428
0.1920155488071286 0.0714285714285712 0.6428571428571428
0.0160851314389874 0.5714285714285713 0.6428571428571428
0.1040503401230580 0.5714285714285713 0.6428571428571428
0.1920155488071286 0.5714285714285713 0.6428571428571428
0.0160851314389874 0.1428571428571427 0.7857142857142857
0.1040503401230579 0.1428571428571427 0.7857142857142857
0.1920155488071285 0.1428571428571427 0.7857142857142857
0.0160851314389874 0.6428571428571427 0.7857142857142857
0.1040503401230581 0.6428571428571427 0.7857142857142857
0.1920155488071286 0.6428571428571427 0.7857142857142857
0.0160851314389874 0.2142857142857142 0.9285714285714285
0.1040503401230580 0.2142857142857142 0.9285714285714285
0.1920155488071286 0.2142857142857142 0.9285714285714285
0.0160851314389874 0.7142857142857140 0.9285714285714285
0.1040503401230579 0.7142857142857140 0.9285714285714285
0.1920155488071286 0.7142857142857140 0.9285714285714285

In this context, the tool utilized symbols such as `+` and `2-` ostensibly to denote the expected ionic states of the elements involved (silver, sulfur, and silicon respectively). However, after reviewing VASP documentation and existing literature, I have not found a clear guideline or precedent for this specific manner of element notation in POSCAR files.

Consequently, I am reaching out to seek your esteemed advice or clarification on several points: 1. Is the notation used above (Ag+ S2- Si) considered valid in POSCAR files when processed by VASP, or should the element specification strictly omit any indication of ionic state? 2. If the notation is indeed invalid, does VASP automatically interpret and adjust ionic states based on the potcar files, rendering explicit ionic state notation unnecessary? 3. Are there recommended practices or modifications for handling ionic states of elements in POSCAR files that I should be aware of to ensure accurate and efficient calculations?

Your insights on these questions would be greatly appreciated, as they will greatly facilitate in ensuring that my computational models are both accurate and in alignment with best practices for using VASP.

Thank you for your time and assistance.

Best regards,
Zhao

[manuel_engel1]

Dear Zhao,

The specification of the POSCAR file is found here on the VASP wiki. From this documentation, we learn the following:

1. The line containing the species names is optional.
2. If given, the species names should match the names and ordering found on the POTCAR file.
3. Each species name on the POSCAR is truncated after two characters.
4. In case of inconsistencies, VASP always uses the species names and ordering from the POTCAR file.

Let's apply this to your example. First, the species names will be truncated:

• Ag+ → Ag
• S2- → S2
• Si → Si

Ag and Si will probably match the POTCAR information exactly, but S2 is most likely not what is found on your POTCAR. In this case, VASP complains with a warning:

Code: Select all

 WARNING: type information on POSCAR and POTCAR are incompatible
 POTCAR overwrites the type information in POSCAR
 typ   2 type information:  S2 S

In the end, VASP will always use the POTCAR information. However for consistency, you should always strive to have the correct type information also on the POSCAR. In this sense, I would say that your POSCAR is not valid, but it will not affect your calculations.
I hope I was able to help with your questions.

Best,
Manuel

[hszhao.cn@gmail.com]

Dear manuel_engel1,

I see. Thank you for your wonderful explanation.

Regards,
Zhao