From owner-chemistry@ccl.net Wed Jan 18 11:09:00 2012 From: "Roger Robinson scu98rkr%a%gmail.com" To: CCL Subject: CCL: G09: CCSD method and large basis Sets Message-Id: <-46161-120118110517-19797-0jtokRp/jbtQJvYadJjo0Q_-_server.ccl.net> X-Original-From: Roger Robinson Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=ISO-8859-1; format=flowed Date: Wed, 18 Jan 2012 16:05:18 +0000 MIME-Version: 1.0 Sent to CCL by: Roger Robinson [scu98rkr^-^gmail.com] Dear All, I want to accurately calculate barrier heights for several sets of reactions. I am looking at molecules up to say 9-10 large atoms + Hydrogens. Currently I am using G09 for my calculations For most of my work I am looking at using the M06-2X functional for calculating geometries, frequencies and zero point energies and for other bits and bobs. I have just about managed to install GAMESS and I am considering maybe the M08-SO functional for future work. But a I also need to calculate the barrier heights with as much precision as possible. I have looked at a few papers such as Kinetics of hydrogen-transfer isomerizations of butoxyl radicals by Zhen and Truhlar They suggest CCSD(T)/CBS+CV+Rel.//M06-2X/MG3S as a very accurate method. Im looking at slightly bigger molecules them and I probably dont have the same resources available as them. I have managed to calculate barrier heights at the CCSD(T)/aug-cc-pVDZ//M06-2X/MG3S level so far. I am currently trying to do so at the CCSD(T)/aug-cc-pVTZ//M06-2X/MG3S level. So far the RWF files have got to ~330GB ! Im not too sure I have the resources to do this. The Timings Comparisons on http://cccbdb.nist.gov/ Seem to suggest VTZ will be 42 slower for a molecule with 3 large atoms, which does nt sound right to me. This might be becuase the examples on http://cccbdb.nist.gov/ run quite quickly so there is alot of I/O activity ? 42 times longer would be well beyond my capabilities. Does anyone have any though on CCSD(T)/maug-cc-pVTZ or CCSD(T)/cc-VTZ. Would CCSD(T)/aug-cc-pVDZ//M06-2X/MG3S be about as accurate as Im going to get for a molecule with 9 carbons ? I can use 12 core machine shared memory machines but Im hoping the jobs last weeks not months. Any help appreciated, Roger