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I'm performing AIMD simulations for a system containing two different types of oxygen atoms: one on the surface and the other outside the surface. To distinguish between them, I labeled the oxygen atoms as "O2" and "O" in the POSCAR file. However, I received the following warning:

"WARNING: type information on POSCAR and POTCAR are incompatible. POTCAR overwrites the type information in POSCAR. typ 3 type information: O2 O."

Is there an alternative way to differentiate between these two types of oxygen atoms for machine learning simulations?

Dear aijitha_john,

Thank you for your question.

It is important that the types in your POSCAR match the types in POTCAR. So if you now have two oxygen types in your POSCAR, you need to have the same in your POTCAR, i.e., copy the oxygen potential twice.

Best wishes,
Alexey

Thanks Alexye,

My POSCAR is like

Title
1.0000000000000000
18.1506171891947687 0.0000000000000000 0.0000000000000000
-9.0753085945974004 15.7188955799581809 0.0000000000000000
0.0000000000000000 0.0000000000000000 25.0000000000000000
C F O2 O Ti
72 36 72 36 107
C
.....

and

grep TITEL POTCAR
gives:
TITEL = PAW_PBE C 08Apr2002
TITEL = PAW_PBE F 08Apr2002
TITEL = PAW_PBE O 08Apr2002
TITEL = PAW_PBE O 08Apr2002
TITEL = PAW_PBE Ti_sv 26Sep2005
I have copied POTCAR for Oxyge twise. Is there any specific keyword I need to add or modify to correct this issue?

What version of VASP are you using? The newest version of VASP can ignore the suffix in the species type, so it should not show this warning. In the older versions, you should specify species as O, not O2. But in principle it is a warning so you will still get the correct results as the elements in your POSCAR and POTCAR indeed match. This warning just means that in this version of VASP type O2 was not correctly interpreted.

I am using vasp version 6.4.3

VASP 6.4.3 should be able to identify these types correctly.
Could you please share the input and output files as described in our forum guidelines?

Dear alexey,
The vasp input files are attached.

Actually, what I said above is not exactly correct. VASP ignores the suffix for elements with two characters. It simply ignores symbols after the second character. In your case the second character is 2, so it tries to match O2 and O. But you can read in the warning message that the elements that couldn't be matched are O and O2, so the results should be correct. We will try to make this string matching mechanism more intelligent.