<div><blockquote style="margin: 0px 0px 0px 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div>DearĀ
<span style="color: rgb(32, 33, 36); font-family: Roboto, Arial, sans-serif; letter-spacing: 0.25px; text-wrap: nowrap;">Steve</span>,</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><span style="color: rgb(227, 227, 227); font-family: "Google Sans", Roboto; font-size: 22px; text-align: center; background-color: rgb(40, 42, 44);">Lois</span><br /></div></blockquote></div>
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