Graphene's Hubbard U and nanotube's U

[ShaHan]

TL;DR

Are graphene and nanotube Hubbard U system and if yes, what's the value

PhysRevLett.106,236805 (2011) seems to state that Graphene has U=9.3eV and PRB 55-R11973 (1997) states that nanotube has U=u/N. However, it's not unusual for them to be hubbard U systems

 

[ShaHan]

Well, graphene do have 4.6eV U and SWCNT have about 7eV U. However, these U are smaller than W. So they are not Hubbard U system