Year

Experimental Method

Theoretical Model

Estimated Band Gap [eV]

Reference

1963

T dependent resistivity

-

0.4

[33]

1979

-

LSDA

0.3

[44]

2001

-

GW

0.8 ± 0.1

[45]

2002

ARPES & RIXS

-

>1.0

[35]

2002

-

GW

0.0

[37]

2003

ARPES

-

1.0

[36]

2004

EELS

LDA**

0

[38]

2004

e-transport, tunneling

-

0.2 and 1.0

[43]

2005

-

sX-LDA

>1.2

[46]

2008

-

QMC

1.3

[39]

2008

-

LSDA

0.2

[40]

2009

-

GGA-HCTH

0.85

[47]