From owner-chemistry@ccl.net Wed Jun 21 10:06:00 2017 From: "Ulrike Salzner salzner a fen.bilkent.edu.tr" To: CCL Subject: CCL: symmetry breaking Message-Id: <-52859-170621100349-13317-J3jW+9AAre+vlJo1hdDM9w+*+server.ccl.net> X-Original-From: Ulrike Salzner Content-Type: multipart/alternative; boundary="94eb2c0877fcaeeabb055278d51a" Date: Wed, 21 Jun 2017 17:03:37 +0300 MIME-Version: 1.0 Sent to CCL by: Ulrike Salzner [salzner:_:fen.bilkent.edu.tr] --94eb2c0877fcaeeabb055278d51a Content-Type: text/plain; charset="UTF-8" Dear Susi, Oleg, ans Mikael, Thank you for your responses, which were very helpful. I have succeeded to find the broken symmetry solutions with wavefunction stability checks. In short, there was no correlation between ease of finding the broken symmetry solution and biradical character of the final broken symmetry solution. There seems to be a correlation with the amount of change in electron density, at least for the few systems I studied. I have a follow-up question: Ess et al. (J. Chem. Phys. A, 2011,115,77) used fractional spin occupation DFT (FS-DFT) to analyze broken symmetry solutions without spin contamination. They start from the closed-shell singlet orbitals and change the occupancies of HOMO and LUMO to 0.5 each, then do a SCF calculation with fixed occupations. I am trying to figure out whether this can give the exact solution as claimed. As the closed-shell orbitals are symmetric, this will not give alpha and beta electrons different space orbitals. In UHF the HOMO and LUMO form linear combinations which allow alpha and beta electron to localize at opposite ends of the molecule. I always considered this as an essential driving force for symmetry breaking. Can anyone comment on this? Thanks, Ulrike -- Assoc. Prof. Ulrike Salzner Department of Chemistry Bilkent University 06800 Bilkent, Ankara --94eb2c0877fcaeeabb055278d51a Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Dear Susi, Oleg, ans Mikael,
<= /div>Thank you for your responses, which were very helpful.
I have= succeeded to find the broken symmetry solutions with wavefunction stabilit= y checks.
In short, there was no correlation between ease of finding the broken=20 symmetry solution and biradical character of the final broken symmetry=20 solution. There seems to be a correlation with the amount of change in=20 electron density, at least for the few systems I studied.
I=20 have a follow-up question: Ess et al. (J. Chem. Phys. A, 2011,115,77)=20 used fractional spin occupation DFT (FS-DFT) to analyze broken symmetry=20 solutions without spin contamination. They start from the closed-shell=20 singlet orbitals and change the occupancies of HOMO and LUMO to 0.5=20 each, then do a SCF calculation with fixed occupations.
I am trying=20 to figure out whether this can give the exact solution as claimed. As=20 the closed-shell orbitals are symmetric, this will not give alpha and=20 beta electrons different space orbitals. In UHF the HOMO and LUMO form=20 linear combinations which allow alpha and beta electron to localize at=20 opposite ends of the molecule.=C2=A0 I always considered this as an=20 essential driving force for symmetry breaking. Can anyone comment on=20 this?
Thanks,
Ulrike

--
Assoc. Prof. Ulrike Salzner
Department of Chemist= ry
Bilkent University
06800 Bilkent, Ankara
--94eb2c0877fcaeeabb055278d51a-- From owner-chemistry@ccl.net Wed Jun 21 16:40:01 2017 From: "Wibe Albert de Jong nwchemex]^[gmail.com" To: CCL Subject: CCL: NWChem developers seeking your input Message-Id: <-52860-170621140843-28910-CrBb7T2Hj1q2gv+hhBcqgg(-)server.ccl.net> X-Original-From: "Wibe Albert de Jong" Date: Wed, 21 Jun 2017 14:08:42 -0400 Sent to CCL by: "Wibe Albert de Jong" [nwchemex ~ gmail.com] Dear users and developers, You are receiving this email because you are on a paper that cited the use of the open- source NWChem computational chemistry software. For the latest developments of the software suite, take a look at http://www.nwchem-sw.org . A US-wide team of developers, including the NWChem team at Pacific Northwest National Laboratory, is embarking on an ambitious effort to build a new, modern C++ based software, ready for a wide variety of computing platforms, including the future exascale supercomputers. This new code will be called NWChemEx. More about this effort can be found on https://www.pnnl.gov/science/highlights/highlight.asp?id=4411 . The goal of the team is to develop an open-source software suite that has the functionality users need, but also resolves any issues that users or developers see with the currently used versions of the NWChem software. Hence, we are seeking your feedback. The NWChemEx team is interesting in receiving your feedback at nwchemex:+:gmail.com on the major pitfalls and issues with, or positive features of NWChem, and also the functionality and development support you need to support your research in the future. If you would like to contribute, please send us an email with your thoughts. Your input is crucial to ensure that NWChemEx can deliver the needs of our user community. With kind regards, NWChem and NWChemEx software development team