Dear Martin,<div><br /></div><div>Thank you for the answer. </div><div><br /></div><div>Unfortunatelly, methods like PBE0 and HSE06 are too expensive for the machine I have.</div><div><br /></div><div>Best Regards,</div><div>Dobromir</div><div><br /></div><div> <br /><br /></div><div class="gmail_quote"><div dir="auto" class="gmail_attr">On Wednesday, January 24, 2024 at 12:56:00 PM UTC+2 Martin Konôpka wrote:<br/></div><blockquote class="gmail_quote" style="margin: 0 0 0 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div dir="ltr"><div>Dear Dobromir,</div><div><br></div><div>The gap much depends on the functional used. If you used PBE, perhaps try to use the hybrid functional PBE0. It usually gives wider gaps.<br></div><div>BTW, as far as I know, Kohm-Sham eigenstates with the exception of the highest occupied one do not have any guaranteed physical meaning. (The highest occupied level should be equal to the minus of the ionisation energy in an ideal DFT, at least for molecules). So, to my knowledge, people try to use such functionals and parametrisations that give them Kohn-Sham gaps equal (approximately) to experimental optical band gaps. I my opinion, this is just a pragmatic approach, not an ab initio one.</div><div><br></div><div>Best regards</div><div>Martin.<br></div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">st 24. 1. 2024 o 11:33 Dobromir A Kalchevski <<a href data-email-masked rel="nofollow">dobro...@gmail.com</a>> napísal(a):<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"></blockquote></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hello,<div><br></div><div>I was trying to find the band gap of a SiC slab (the surface is cut by the {111} orientation) and the result is always wrong (the band gap is way too small), due to (as far as my understanding goes) spurious interaction among surface states. I know that terminating the surface dangling bonds/free electrons with H atoms should help, but I am worried that the H will alter the crystal too much. Is there another way to do it ?</div><div><br></div><div>Currently the system is 12 Si atoms, 12 C atoms and H-terminated "bottom" surface. I am using the periodic Poisson solver in 3D, while leaving enough space in the direction perpendicular to the surface.</div><div><br></div><div>Best Regards,</div><div>Dobromir</div><div><br></div><div> </div>
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