<br clear="all"><div>Dear sir,</div><div><br></div><div><b><tt style="margin:0px;font-family:courier,'courier new',monospace;font-size:14px;line-height:19px;background-color:rgb(255,255,255)">I thought your material has a gap, and the question was only direct or </tt><tt style="margin:0px;font-family:courier,'courier new',monospace;font-size:14px;line-height:19px;background-color:rgb(255,255,255)">indirect .. ??</tt></b></div>
<div><br></div><div>If i did the calculations using the structure stimulated from the space group (225), it shows a negative indirect band gap in the band structure (negative indirect band gap means, the valance band maximum falls above the Fermi level at gamma point and conduction band minimum falls below the Fermi level at X-point ). Then, can i expect an intra-band contribution to my optical property. Does it give any finite value of plasma frequency in the indirect band gap case...?</div>
<div><br></div><div>At present, i did optical calculations on the primitive cell of same structure where i could find the band folding across the Fermi level. Here, At gamma point, both the valance band maximum falls above the Fermi level and conduction band minimum falls below the Fermi level, showing a direct overlap between them due to band folding. As suggested by your reply, the back folding of bands will not effect the system optical properties. Then, this case is also similar to be a negative indirect band gap like. </div>
<div><br></div><div>So, what is importance of direct, indirect and negative indirect band gaps while calculating the optical properties....may be i should need some examples of experimental data to understand this. Can you suggest me some references. </div>
<div><br></div><div>Looking forward to your answers and comments.</div><div><br></div><div>thanks for your contributions....</div><div><br></div><div>regards, </div><div><br></div><div>venkatesh</div><div><br></div>