<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman,new york,times,serif;font-size:12pt"><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;">Dear Gabriele and smogunov,<br>Yes, I do use Al- wire of finite width as reported in smogunov's 2004 paper. In this case what should be the k-pt grid for scf calculation? {for conductance calculation k_perp is set to 1} <br>When doing calcuIation with electrode infinite in xy plane, is it necessary to use same k-pt grid for conductance and scf calculation?<br>When doing PDOS calculation of molecule, is the gamma point calculation sufficient?<br><br>Thanking you.<br><br>Sagar Ambavale<br><br>----------------------------------------------------------------------<br><br>Message: 1<br>Date: Mon, 15 Jun 2009 09:04:03 +0200<br>From: Gabriele Sclauzero
<<a ymailto="mailto:sclauzer@sissa.it" href="mailto:sclauzer@sissa.it">sclauzer@sissa.it</a>><br>Subject: Re: [Pw_forum] homo-lumo and conductance<br>To: PWSCF Forum <<a ymailto="mailto:pw_forum@pwscf.org" href="mailto:pw_forum@pwscf.org">pw_forum@pwscf.org</a>><br>Message-ID: <<a ymailto="mailto:4A35F263.9020205@sissa.it" href="mailto:4A35F263.9020205@sissa.it">4A35F263.9020205@sissa.it</a>><br>Content-Type: text/plain; charset=ISO-8859-1; format=flowed<br><br><br><br>ambavale sagar wrote:<br>> Dear Gabriele,<br>> Thank you for your reply. I refered to smogunov paper but I could not <br>> understand the sentence used there : "Since the system has the supercell <br>> (artificial) 2D periodicity in the xy plane, perpendicular to the <br>> transport direction, we averaged the transmission over the corresponding <br>> 2D BZ using 21 k points in the irreducible part of the BZ.." Are those <br>> 21 k-pts belong to
xy plane only? what type of grid that may be? 6 6 2 1 <br>> 1 1 ?<br>> In my case supercell dimensions in x and y are 25 a.u. i.e. ~12 ang <br>> which includes nearly ~9 ang. of vaccum.<br><br>Here Alexander already replied you. So your k_perpendicular points sampling depends if you <br>want to study an isolated wire (thick or monoatomic), or a wire/molecule between realistic <br>electrodes (modeled as surfaces or surfaces+tips attached to them). In the former case, if <br>your supercell is large enough in the directions perpendicular to the transport the <br>transmission should not depend on k_perp and you need only one k_perp-point. In the latter <br>you need to sample accurately the 2D BZ, since the transmission depends (a lot in some <br>cases) on k_perp.<br><br>> <br>> As you mentioned the limitation of DFT due to xc-functional, can I use <br>> DFT calculation to compare qualitatively the Transmission coefficient of <br>> same
molecule with different geometries?<br><br>I cannot say, actually. It depends on the coupling and other details. You can have a look <br>to the recent work by Thygesen and Rubio, which try to include a GW correction in this <br>kind of calculations.<br><br>> <br>> would you please mention in detail how to find positions of HOMO, LUMO <br>> in a coupled system?<br><br>What I would do (but fur sure there are many better methods) if I want to put, say, O_2 <br>between electrodes is to look at the PDOS (computed by projwfc.x in the QE suite) <br>projected onto the O atoms and compare it with the PDOS of the isolated O_2. It would give <br>an idea of the level of hybridization between molecule and electrodes and of the position <br>of the HOMO(LUMO)-derived levels.<br>It could also be useful to look at the PDOS on the electrode atoms to understand which <br>metallic states/atoms are more involved in the
coupling.<br><br>regards,<br><br>GS<br><br><br><br></div></div></div><br>
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