From owner-chemistry@ccl.net Mon Jul 3 09:45:01 2017 From: "Norrby, Per-Ola Per-Ola.Norrby.:.astrazeneca.com" To: CCL Subject: CCL:G: Unrestricted vs. restricted DFT for closed-shell metal complex Message-Id: <-52870-170703014257-2567-Qeq2PvqHHvZSyYrXLgBONA^server.ccl.net> X-Original-From: "Norrby, Per-Ola" Content-Language: en-US Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="us-ascii" Date: Mon, 3 Jul 2017 05:42:33 +0000 MIME-Version: 1.0 Sent to CCL by: "Norrby, Per-Ola" [Per-Ola.Norrby]|[astrazeneca.com] Hi Andrew, You can easily test if the system has a preference for an open-shell solution, for example by using the "Stable" keyword in Gaussian. Alternatively, you can try to run an unrestricted calculation, but then you MUST start from a wave-function where the alpha and beta are different. You can generate such a state by mixing HOMO and LUMO, for example, but I find that the safest way is to first run an unrestricted triplet calculation, and then use that wave function as the starting guess for the unrestricted singlet. If you want to bias towards open-shell solution, you can even start from the triplet geometry, not the restricted singlet geometry. If you have trouble converging, and use Jaguar, I often use the "RO" instead of "U" to get a good starting point, but I switch to "U" for the final energies. In Gaussian (and most other programs), I'd stay with "U" throughout. Note that if you DO find a stable, unrestricted open shell singlet solution, you have opened a can of worms. You'll have to use some broken symmetry correction, but I'm not fully up to date on which approach is best. The intuitively simplest is to also calculate the triplet at the same geometry, and assume that your unrestricted singlet calculation is in reality halfway between the triplet and the true open shell singlet. That is, what you have is "ab", triplet is "ab+ba" = "aa" = "bb", true singlet is "ab-ba", but this is only a simplified solution. Some programs, like Jaguar, will allow you (with some keyword fiddling) to actually use a double determinant, going directly for the "ab-ba" solution. I don't know the quality within the DFT framework though. I've had similar problems for Cu, Mn, and Cr, long ago. We started B3LYP, found that the "same" DFT calculation could give very different results depending on starting guess (created by manual rotations of high spin starting guesses), then went down the CASPT2 path to help us sort through the data, never reached publication stage though. Cheers, Per-Ola -----Original Message----- > From: owner-chemistry+per-ola.norrby==astrazeneca.com=ccl.net [mailto:owner-chemistry+per-ola.norrby==astrazeneca.com=ccl.net] On Behalf Of Andrew Scott Rosen rosen^u.northwestern.edu Sent: den 2 juli 2017 06:57 To: Norrby, Per-Ola Subject: CCL:G: Unrestricted vs. restricted DFT for closed-shell metal complex Sent to CCL by: "Andrew Scott Rosen" [rosen]^[u.northwestern.edu] Hello, I have a question regarding the choice of unrestricted versus restricted calculations in DFT. Let's say that I am dealing with a Cu(I) organometallic complex that I anticipate would have a spin multiplicity of 1 due to the assumed [Ar]3d10 electron configuration of Cu(I) in this complex. Under this assumption, the system is not open-shell. As such, it seems that a restricted calculation would be most appropriate. Would there be any benefit in running an unrestricted calculation (still as a singlet) in this case? Additionally, what would an unrestricted calculation on a system that's a singlet even mean, especially if I don't use specific keywords (e.g. in Gaussian) to try and obtain a broken- symmetry state? To provide context, I ask because I start with a Cu(II) complex that reduces to a Cu(I) complex. I do an unrestricted calculation when modeling the Cu(II) complex, and I want to compute the energy of the resulting Cu(I) complex for comparison. Thank you greatly for any input. Best regards, 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If you have received this message in error, please notify us and remove it from your system and note that you must not copy, distribute or take any action in reliance on it. Any unauthorized use or disclosure of the contents of this message is not permitted and may be unlawful. From owner-chemistry@ccl.net Mon Jul 3 10:20:00 2017 From: "Jan Jensen compchemhighlights##gmail.com" To: CCL Subject: CCL: Computational Chemistry Highlight: June issue Message-Id: <-52871-170703033001-2568-tkhyhQDSe/8dvY8UTYIxkA(!)server.ccl.net> X-Original-From: Jan Jensen Content-Type: multipart/alternative; boundary="f403045dd5b0cd9ff4055364bb4f" Date: Mon, 3 Jul 2017 09:29:55 +0200 MIME-Version: 1.0 Sent to CCL by: Jan Jensen [compchemhighlights**gmail.com] --f403045dd5b0cd9ff4055364bb4f Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable The June issue of Computational Chemistry Highlights is out. CCH is an overlay journal th= at identifies the most important papers in computational and theoretical chemistry published in the last 1-2 years. CCH is not affiliated with any publisher: it is a free resource run by scientists for scientists. You can read more about it here . Table of content for this issue features contributions from Steven Bachrach and Jan Jensen: A Deep Neural Network with Minimal Chemistry Knowledge Matches the Performance of Expert-developed QSAR/QSPR Models London Dispersion Enables the Shortest Intermolecular Hydrocarbon H=C2=B7= =C2=B7=C2=B7H Contact. Dynamic Effects Responsible for High Selectivity in a [3,3] Sigmatropic Rearrangement Featuring a Bispericyclic Transition State Interested in contributing? Read more here Interested in more? There are many ways to subscribe to CCH updates . Also, for your daily computational chemistry fix subscribe to Computational Chemistry Daily --f403045dd5b0cd9ff4055364bb4f Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

The June issue of=C2=A0Computati= onal Chemistry Highlights=C2=A0is out.

CCH is an=C2=A0overlay journal=C2=A0that identif= ies the most important papers in computational and theoretical chemistry pu= blished in the last 1-2 years. CCH is not affiliated with any publisher: it= is a free resource run by scientists for scientists.=C2=A0You can read more about it here.


Table of content for t= his issue features contributions from Steven Bachrach and Jan Jensen:


A Deep Neural Network with Minimal Chemistry Knowledge Matches = the Performance of Expert-developed QSAR/QSPR Models



Dynamic Effects Responsible for High Selectivity i= n a [3,3] Sigmatropic Rearrangement Featuring a Bispericyclic Transition St= ate


Int= erested in contributing? =C2=A0Read more here


Interested in more?=C2=A0There ar= e many ways to subscribe to CCH updates.


Also, for your daily computational chemis= try fix subscribe to=C2=A0Computational Chemistry Daily

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