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Dear Joseph,
you can try out our recently developed HF-3c method. It is based on a HF/minimal(small) basis set calculation and therefore fast. Three atom pair-wise correction terms are applied to correct the HF energy with respect to London dispersion interactions (D3 scheme), basis set superposition error (gCP scheme), and short-ranged basis set incompleteness effects. More details can be found in the publication: J. Comput. Chem. 34, 1672–1685 (2013) The HF-3c method yields good geometries for standard organic molecules, supramolecules and proteins. HF-3c is implemented in the free ORCA software suite. You can simply invoke it by the keyword ! HF-3c. As you cannot use our method with G09 you would have to switch to a different program but it is probably worth trying. Cheers, Rebecca --
Rebecca Sure, M.Sc. (rebecca.sure=-=thch.uni-bonn.de On 06/20/2013 02:54 AM, Joseph Takayama sjtakayama*|*gmail.com wrote: Sent to CCL by: "Joseph Takayama" [sjtakayama-*-gmail.com] Hi Everyone, I'm trying to optimize some transition state structure with B3LYP/6-31G*. I'd like to do pre-optimization in order to shorten the calculation time and see if my initial structure works. I might need to do some try & error, so I'd like to shorten the calculation time as much as possible for pre-optimization. Among the following options, which do you think is acceptable? 1. Change method to HF, AM1 or PM3. 2. Change basis function to 3-21G* or to STO-3G. 3. Add SCF=(conver=4) 4. Add opt=loose. 5. Is there any other way to reduce calculation time?? I'm using Gaussian 09 and my main targets are organic molecule just contains H,C,N,O atoms and inorganic complex contains one transition metal.E-mail to subscribers: CHEMISTRY=-=ccl.net or use: http://www.ccl.net/cgi-bin/ccl/send_ccl_message E-mail to administrators: CHEMISTRY-REQUEST=-=ccl.net or use http://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtml Before posting, check wait time at: http://www.ccl.net Job: http://www.ccl.net/jobs Conferences: http://server.ccl.net/chemistry/announcements/conferences/ Search Messages: http://www.ccl.net/chemistry/searchccl/index.shtmlhttp://www.ccl.net/spammers.txt RTFI: http://www.ccl.net/chemistry/aboutccl/instructions/ |