How to filter materials

Example filter strings:

filter	meaning
Cu>1	more than 1 Cu atom
gap>1.1	“gap” larger than 1.1
xc=PBE	“xc” equal to “PBE”
MoS2	one or more MoS2 formula units
Mo	same as Mo>0 or Mo!=0
gap	material has key named gap

Strings can be combined with “,” (and) and “|” (or). Use “~” for “not”. “Grouping can be done using “(” and “)”:

filter	meaning
Au, O=0	contains gold but no oxygen
~(Au=0 | O)	same as above
Cu | Fe	contains Cu or Fe
gap>1.1, (Cu | Fe)	band gap larger than 1.1 and contains Cu or Fe
(C|Si|Ge|Sn),Pb=0,nspecies=3	contains C, Si, Ge or Sn, no Pb and 3 species
~gap	material has no key named gap