From owner-chemistry@ccl.net Sun Jul 2 17:58:01 2017 From: "Susi Lehtola susi.lehtola/./alumni.helsinki.fi" To: CCL Subject: CCL:G: Unrestricted vs. restricted DFT for closed-shell metal complex Message-Id: <-52868-170702143442-5621-rVXS/CMhu+mEWmFn4fN7qA*server.ccl.net> X-Original-From: Susi Lehtola Content-Language: en-US Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=utf-8; format=flowed Date: Sun, 2 Jul 2017 11:34:28 -0700 MIME-Version: 1.0 Sent to CCL by: Susi Lehtola [susi.lehtola,alumni.helsinki.fi] On 07/01/2017 09:56 PM, Andrew Scott Rosen rosen^u.northwestern.edu wrote: > > 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? If you run spin-unrestricted DFT with a spin-restricted guess, you'll get the same solution as with spin-restricted DFT, only getting it will be 2-3x more expensive. This is because there's nothing that will break the alpha-beta spin symmetry: a restricted guess gives identical alpha and beta Fock matrices, and consecutively identical new alpha and beta orbitals. -- ----------------------------------------------------------------------- Mr. Susi Lehtola, PhD Chemist Postdoctoral Fellow susi.lehtola##alumni.helsinki.fi Lawrence Berkeley National Laboratory http://www.helsinki.fi/~jzlehtol USA -----------------------------------------------------------------------