From owner-chemistry@ccl.net Mon Dec 30 12:38:00 2013
From: "Johan Paul yt1388{}gmail.com" <owner-chemistry^_^server.ccl.net>
To: CCL
Subject: CCL: Usage of X-ray structure for DFT calculations
Message-Id: <-49487-131230113246-19500-wQJL9HWpXDVsGfyOXRfi/w^_^server.ccl.net>
X-Original-From: "Johan  Paul" <yt1388.^_^.gmail.com>
Date: Mon, 30 Dec 2013 11:32:44 -0500


Sent to CCL by: "Johan  Paul" [yt1388(!)gmail.com]
Dear all,

I submitted a paper (combined theoretical and experimental) to a journal. However, the referee didn't accept the comparisons mentioning that "you can not compare the two structural parameters". I did such comparisons before. What factors are mainly affecting the comparison between the x-ray structure and the DFT optimized structures? BTW, I used both gas phase optimizations as well as solvent calculations using polar solvents since I have chromophors at the structural backbone. 
Any comments and suggestions are appreciated. 

Best regards,
Johan Paul


From owner-chemistry@ccl.net Mon Dec 30 13:36:01 2013
From: "Stefan Grimme grimme=thch.uni-bonn.de" <owner-chemistry+/-server.ccl.net>
To: CCL
Subject: CCL: Usage of X-ray structure for DFT calculations
Message-Id: <-49488-131230133217-18386-JuTdBQlAwEamcQk8duHl8A+/-server.ccl.net>
X-Original-From: "Stefan  Grimme" <grimme^^^thch.uni-bonn.de>
Date: Mon, 30 Dec 2013 13:32:15 -0500


Sent to CCL by: "Stefan  Grimme" [grimme,+,thch.uni-bonn.de]
Dear Johan Paul,
indeed the referee is right that any theoretical, isolated molecular structure can not directly be compared to those of a molecular crystal because the latter
is influenced by intermolecular interactions of various type,
namely Pauli-repulsion, induction, electrostatics, and dispersion
("packing forces"). If these (and further thermal) effects are significant (rarely) or negligible (the more frequent case) depends on the system (and in particular on charges/counter-ions). We recently investigated a difficult case by molecular and periodic DFT-D3 calculations: 
	
J. Moellmann and S. Grimme, Influence of Crystal Packing on an Organometallic Ruthenium(IV) Complex Structure: The Right Distance for the Right Reason, Organometallics, (2013), 32, 3784-3787. DOI: 10.1021/om400386x

For a very recent unbiased and fair benchmark of organic molecule gas phase structures by experiment and DFT see:

S. Grimme, M. Steinmetz, Effects of London dispersion correction in density functional theory on the structures of organic molecules in the gas phase, Phys. Chem. Chem. Phys., (2013), 15, 16031-16042. DOI: 10.1039/c3cp52293h

Hope this helps
Stefan