The ABINIT Users Mailing List ( CLOSED )

[Geoffrey Stenuit <geoffrey.stenuit@tyndall.ie>]

Dear Xiao Deng,

The problem of the coupling between the CB and the VB depends for me on
the material. For example, the underestimation of the LDA energy gap for
Si and Ge doesn't affect the LDA effective masses, which iare in good
agreement with the experimental one. On the other hand, such coupling
reduces the effective mass of GaAs, particulary if you include the Ga
(3d) state in your pseudopotential as valence electron. Therefore, if
your material exhibits a too strong coupling, i would advise you to use
an Empirical Pseudo-Potential approach (see for example: Cohen and
Chelikowsky, Electronic Structure and optical Properties of
Semiconductors, Springer Series; L. Bellaiche et. al. PRB54, 17568 (1996))

Good luck again,

Joe

zzzhong wrote:

>Dear abinit user,hello!
>     About the effective mass, I have some questions. Because the LDA 
> underestimate the energy gap(Eg). the couple between the conduction band 
> and the valence band  is modified. I am afraid that the effective mass of 
> the electron in the Gamma point is underestimate. Maybe the GW caculation 
> can resolve this problem. But for the big supercell, the GW calculation is 
> a big problem. Do we have another method to resolve this problem.  
>       
>
>======= 2006-11-21 20:07:51 您在来信中写道：=======
>
>  
>
>>On 21 Nov 2006, at 12:27, Geoffrey Stenuit wrote:
>>
>>    
>>
>>>Xiao Deng wrote:
>>>
>>>      
>>>
>>>>Dear abinit user,
>>>>       I want to get the effective mass of the electrons and  
>>>>holes. Can anybody give me some advice? Thanks!
>>>> Xiao Deng
>>>>        
>>>>
>>>Dear Xiao Deng,
>>>
>>>An easy way to get the effective mass is simply to compute the  
>>>energy dispersion in the vicinity of the k-point where you would  
>>>like to calculate the mass (See the abinit tutorial, lesson 3 for  
>>>more details about the computation of the band structure). Using  
>>>the relation,
>>>$E(k)=\frac{\hbar^2k^2}{2m^*}$,
>>>you then need to fit the energy dispersion with a quadratic law $E 
>>>(k)=Ck^2$, the quadratic coefficient C being inversely proportional  
>>>to the effective mass.
>>>
>>>Good luck,
>>>
>>>Joe
>>>      
>>>
>>RIght. Note however the following subtlety : the number of planewaves  
>>may vary
>>with the k point, causing some numerical noise. To avoid this noise  
>>in the eigenenergy curves, simply
>>use a non-zero ecutsm (the recommended value of 0.5 Ha should be OK).
>>
>>Xavier
>>    
>>
>
>= = = = = = = = = = = = = = = = = = = =
>   Best regards
>                                
>　 zzzhong
>   State Key Laboratory for Superlattices and Microstructures
>　 Institute of Semiconductors
>   Chinese Academy of Sciences
>   P. O. Box 912, Beijing 100083
>　 Eamil: zzzhong@red.semi.ac.cn
>　 2006-11-22
>
>
>
>
>  
>