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QuantumATK => General Questions and Answers => Topic started by: Ash on June 11, 2012, 06:05

Title: Variation of E-k diagram for the smallest unit cell to large unit cell bulk?
Post by: Ash on June 11, 2012, 06:05

Hi everyone,
Can someone help me explain the variation of band gap value (Eg), its location with respect to Fermi level, the curvature of valence band minimum and conduction band maximum  and number of valence (conduction) bands below (above) the Fermi level as the bulk grows from smallest unit cell to the unit cell containing more number of smallest unit cells ?

Title: Re: Variation of E-k diagram for the smallest unit cell to large unit cell bulk?
Post by: zh on June 12, 2012, 14:03

For a perfect semiconductor or insulator system, the value of band gap and the location of band gap with respect to the Fermi level do not change with respect to the size of unit cell.

Since the curvatures of valence band minimum of conduction band maximum correspond to the effective mass of electron or hole, they do not vary with the use of different size of unit cell. 

Since the number of atoms in the unit cell depends on the size of unit cell,  the number of valence bands below the Fermi level will vary with the size of unit cell. However, the number of conduction bands above the Fermi level is not a physical quantity of interest.

Title: Re: Variation of E-k diagram for the smallest unit cell to large unit cell bulk?
Post by: Ash on June 12, 2012, 15:24

Thanks Zh !! for your detailed and helpful reply  :)