How to use SE(extended-huckel) to optmize geometry ?

[fangyongxinxi]

Dear Sir,
I hope to optmize one configuration(200 atoms) by ATK12.8. When doing script generator, I choose the 'calculator' with SE(extended-huckel), the "optmizegeometry" can not be choose. So, my question is : the SE(extended-huckel) method is not be able to do the optmize work?
If I want to optmize this configuration, what I should do ?

Thanks.

[Anders Blom]

As you noted, the extended Huckel calculator in ATK does not support calculation of forces and stress since there is no pair potential defined in the method. You must use DFT instead, or perhaps a DFTB or other Slater-Koster model in ATK-SE for the geometry optimization.