From owner-chemistry@ccl.net Tue Sep 22 13:23:01 2015 From: "Frank Jensen frj++chem.au.dk" To: CCL Subject: CCL: The use of NMR spectra computations for verification of computational method Message-Id: <-51766-150922132155-27478-ozbKPj+hPPU8JvLVWHrDrQ%x%server.ccl.net> X-Original-From: Frank Jensen Content-Language: en-US Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="us-ascii" Date: Tue, 22 Sep 2015 17:21:46 +0000 MIME-Version: 1.0 Sent to CCL by: Frank Jensen [frj++chem.au.dk] A few selected references for a start: > From CCSD(T)/aug-cc-pVTZ-J to CCSD(T) complete basis set limit isotropic nuclear magnetic shieldings via affordable DFT/CBS calculations By: Kupka, Teobald; Stachow, Michal; Nieradka, Marzena; et al. MAGNETIC RESONANCE IN CHEMISTRY Volume: 49 Issue: 5 Pages: 231-236 Published: MAY 2011 Benchmarking Hydrogen and Carbon NMR Chemical Shifts at HF, DFT, and MP2 Levels By: Flaig, Denis; Maurer, Marina; Hanni, Matti; et al. JOURNAL OF CHEMICAL THEORY AND COMPUTATION Volume: 10 Issue: 2 Pages: 572-578 Published: FEB 2014 Benchmarking density-functional theory calculations of NMR shielding constants and spin-rotation constants using accurate coupled-cluster calculations By: Teale, Andrew M.; Lutnaes, Ola B.; Helgaker, Trygve; et al. JOURNAL OF CHEMICAL PHYSICS Volume: 138 Issue: 2 Article Number: 024111 Published: JAN 14 2013 Segmented Contracted Basis Sets Optimized for Nuclear Magnetic Shielding By: Jensen, Frank JOURNAL OF CHEMICAL THEORY AND COMPUTATION Volume: 11 Issue: 1 Pages: 132-138 Published: JAN 2015 Frank Frank Jensen Assoc. Prof., Vice-Chair Dept. of Chemistry Aarhus University http://old.chem.au.dk/~frj -----Original Message----- > From: owner-chemistry+frj==chem.au.dk^-^ccl.net [mailto:owner-chemistry+frj==chem.au.dk^-^ccl.net] On Behalf Of Grigoriy Zhurko reg_zhurko : chemcraftprog.com Sent: 22. september 2015 16:12 To: Frank Jensen Subject: CCL: The use of NMR spectra computations for verification of computational method Sent to CCL by: Grigoriy Zhurko [reg_zhurko||chemcraftprog.com] > Sent to CCL by: Frank Jensen [frj * chem.au.dk] One cannot help > wondering why people still are using B3LYP/6-31G* as the answer to any question. > For NMR shielding, there are better functionals and basis sets optimized specifically for NMR. > Using such a combination will have essentially the same computational > cost, and who knows, may even solve problems like the one posed. 1) So, what are these functionals and basis sets? 2) I still need to know, whether the B coefficient in Y=A+B*X equation of the correlation must be equal 1. > Frank > Frank Jensen > Assoc. Prof., Vice-Chair > Dept. of Chemistry > Aarhus University > http://old.chem.au.dk/~frj > -----Original Message----- >> From: owner-chemistry+frj==chem.au.dk::ccl.net >> [mailto:owner-chemistry+frj==chem.au.dk::ccl.net] On Behalf Of >> Grigoriy Zhurko reg_zhurko^chemcraftprog.com > Sent: 21. september 2015 19:20 > To: Frank Jensen > Subject: CCL: The use of NMR spectra computations for verification of > computational method > Sent to CCL by: Grigoriy Zhurko [reg_zhurko^chemcraftprog.com] I have > been computing NMR spectra of several organic compounds, comparing > them with the experiment. Usually these computations show big > systematic errors, but correlate well with the experiment (for > C13 spectra of organic molecules, I got the correlation coefficient R > about 0.9995 with B3LYP/6-311G(D,P) method). > Now I have computed some NMR spectra of bilirubin molecule with > different DFT functionals, and I found that the correlation > coefficient is not a good criteria of computation accuracy in my case. > This molecule has internal hydrogen bonds, and different functionals > (in particular, B3LYP and PBE) give quite different O..H distance (the > difference is about 0.1 A), while other bond lengths in this molecule > do not differ significantly (the difference is > 0.012 A or less). The PMR spectrum with B3LYP correlates with the > experimental one with R=0.997, and with PBE ? R=0.995. These values do > not differ very much. But the coefficient B in the equation Y=A+B*X > (for the linear approximation of experiment vs theory graph) is 1.02 > for B3LYP, and 1.14 for PBE. So, with PBE it is far less from 1. Does > that mean that PBE is much less appropriate method for this task? > I suppose, that the systematic error of absolute values of the NMR > chemical shifts is caused by unclear physical meaning of these > chemical shifts and shieldings (maybe the solvent gives some > additional shielding in experiment). So, my question is, whether the B > coefficient in correlation must be always equal 1. If yes, then > instead of correlation coefficients R I should use another criteria of > computation accuracy ? the RMS of MAE difference between the computed > and experimental chemical shifts, if the shielding of the standard > (TMS) simply fitted for best agreement (not computed > quantum-chemically). Is that correct? In my case, these MAE difference > must be much bigger for PBE functional, than for the B3LYP functional.http://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt