About the POTCAR versions used in keys of functional_dir dictionary without version numbers.

[hongyi-zhao]

As shown below, there are some keys used in functional_dir dict which don't include version numbers in their names, aka, PBE, LDA and LDA_US:

pymatgen/src/pymatgen/io/vasp/inputs.py

Lines 1757 to 1774 in d77f776

	functional_dir: ClassVar[dict[str, str]] = {
	"PBE": "POT_GGA_PAW_PBE",
	"PBE_52": "POT_GGA_PAW_PBE_52",
	"PBE_52_W_HASH": "POTPAW_PBE_52",
	"PBE_54": "POT_GGA_PAW_PBE_54",
	"PBE_54_W_HASH": "POTPAW_PBE_54",
	"PBE_64": "POT_PAW_PBE_64",
	"LDA": "POT_LDA_PAW",
	"LDA_52": "POT_LDA_PAW_52",
	"LDA_52_W_HASH": "POTPAW_LDA_52",
	"LDA_54": "POT_LDA_PAW_54",
	"LDA_54_W_HASH": "POTPAW_LDA_54",
	"LDA_64": "POT_LDA_PAW_64",
	"PW91": "POT_GGA_PAW_PW91",
	"LDA_US": "POT_LDA_US",
	"PW91_US": "POT_GGA_US_PW91",
	"Perdew_Zunger81": "POT_LDA_PAW",
	}

So, I would like to know, when using these keys to set the user_potcar_functional or potcar_functional, what exact versions of the corresponding POTCARs should be used?

Regards,
Zhao

[DanielYang59]

Hi,

I think this is very similar to #3951. functional_dir provides a mapping from the functional you pick (dict key) to the local directory (dict value) where pymatgen would try to search for POTCARs:

pymatgen/src/pymatgen/io/vasp/inputs.py

Lines 2278 to 2279 in b28c937

	functional_subdir = SETTINGS.get("PMG_VASP_PSP_SUB_DIRS", {}).get(functional, cls.functional_dir[functional])
	PMG_VASP_PSP_DIR = SETTINGS.get("PMG_VASP_PSP_DIR")

I.e. you get whatever you put at the nominated location.

[hongyi-zhao]

However, in reality, we all name these directories based on specific versions, so is it meaningful to do so?

[DanielYang59]

Emm... Looks like that's one of the most ancient piece of code of pymatgen (added in b2948d7 2011), and my guess is (I could be wrong here):

• POT_GGA_PAW_PBE/POT_LDA_PAW are the default VASP PSP directory name (I failed to find a PSP directory naming convention from VASP wiki; also I'm not sure if that's the case for all versions of VASP), and it would therefore be a good default location to search
• VASP 5.4.4 was not released back that time (released in 2017), and backward compatibility is certainly playing a part here (we cannot change the default dir from POT_GGA_PAW_PBE to POT_GGA_PAW_PBE_XX after a new VASP release which would cause breakage)