From owner-chemistry@ccl.net Fri Sep 25 12:14:00 2020 From: "Jens Spanget-Larsen spanget__ruc.dk" <owner-chemistry^server.ccl.net> To: CCL Subject: CCL: SV: Intramolecular H-bonding and DFT-D Message-Id: <-54178-200925121231-7497-eFNcstYRmfpuOYgahVEmUA^server.ccl.net> X-Original-From: Jens Spanget-Larsen <spanget##ruc.dk> Content-Language: da-DK Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="us-ascii" Date: Fri, 25 Sep 2020 16:12:22 +0000 MIME-Version: 1.0 Sent to CCL by: Jens Spanget-Larsen [spanget(_)ruc.dk] Dear Stefan, thank you for your overview! Yours, Jens >--< ________________________________________ Fra: owner-chemistry+spanget==ruc.dk##ccl.net [owner-chemistry+spanget==ruc.dk##ccl.net] på vegne af Stefan Grimme grimme#,#thch.uni-bonn.de [owner-chemistry##ccl.net] Sendt: 23. september 2020 17:54 Til: Jens Spanget-Larsen Emne: CCL: Intramolecular H-bonding and DFT-D Sent to CCL by: "Stefan Grimme" [grimme(-)thch.uni-bonn.de] Dear Jens, I'm not aware of a benchmark study to this specific question but please allow me to give a general answer. Dispersion corrections very generally improve the PES for inherently overrepulsive (dispersion devoid) functionals giving better energies, structures and frequencies. There is no physical reason why the intramolecular situation is different from the intermolecular one. However, functionals which at intermediate distances account for some "dispersion type" correlation like e.g. PBE or LDA systematically yield too strong hydrogen bonds and consequently too large vibrational red shifts (partially due to artificial CT). In such cases adding the "-D" in whatever form would further (wrongly) strengthen the bonding. For proper choices like BLYP, TPSS, B3LYP or similar I don't expect any problem. Best Stefanhttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt