CCL: The use of NMR spectra computations for verification of computational method

 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