CCL:G: PBC calculations with gaussian

["Aron Walsh" <aronjwalsh*gmail.com>]

 Hi Tian,

I have never used PBC in gaussian, but it is possible to have a
 lower LUCO than HOCO, i.e. if the valence band maximum occurs at one point in
 reciprocal space, but the conduction band minimum occurs at another point (and
 is lower in energy). For this case you could have both a positive direct gap
 (vertical excitation), and negative indirect gap (such is the case for rocksalt
 CdO at the LDA/GGA level).  
 
I would suggest to plot a band structure to really understand what is going
 on. 

Best,
Aron

On Fri, Oct 31, 2008 at 6:18 PM, Green Power powergreen##gmail.com <owner-chemistry{}ccl.net> wrote:

Hi, All,
I am doing PBC calcualtions on a semi-conducting or conducting polymer. The intermediate output file indicates that the energy level of HOCO is much higher than LUCO. It seems that there is something wrong with the calculation.  Is gaussian program able to deal with electrical conducting systmes?  The following is the energy gaps of the outfile grepped with word "gap". I appreciate your comments and suggestions.

 Alpha HOCO: -10.106346 LUCO:  -9.760573 indirect gap:   0.345773 direct gap:   0.345773 (eV)
 Alpha HOCO:  -5.254607 LUCO:  -7.137990 indirect gap:  -1.883383 direct gap:   0.439553 (eV)
 Alpha HOCO: -42.188484 LUCO: -45.823242 indirect gap:  -3.634758 direct gap:   0.926315 (eV)


Tian