CCL: Differences between theoretical and experimental torsion angles

 Sent to CCL by: Susi Lehtola [susi.lehtola^alumni.helsinki.fi]
 On Sat, 9 Nov 2013 19:58:00 -0500
 "Hamid Shojaei Shojaei81..gmail.com"
 <owner-chemistry.++.ccl.net> wrote:
 >
 > Sent to CCL by: "Hamid  Shojaei" [Shojaei81-#-gmail.com]
 > Dear All,
 >
 > I do some structural calculations but I see big differences between
 theoretical
 > and experimental torsion angles.
 >
 > Torsion angle	       Experimental	Theoretical
 > N(2)C(2)C(3)C(8)	 175.1	        -175.965
 > O(1)C(2)C(3)C(4)	 178.94	        -177.005
 > C(8)C(3)C(4)N(3)	177.0          179.837
 > C(2)C(3)C(4)C(5)	 178.73	        -177.808
 > C(31)N(3)C(4)C(3)	 174.2	         169.686
 > C(4)N(3)C(31)C(32)	  91.0	         138.193
 >
 >
 > Any idea explaining such a differences is highly appreciated.
 You don't mention anything about the level of theory or the basis set
 used, which would be paramount to determine if your calculations are
 correct. Also knowing something about the system could be of used.
 But, there's probably a very simple explanation - you are really
 comparing two different systems: the experiment and calculations are on
 two different conformers. Redo the structural optimization, but change
 the starting point to be more similar to the experimental geometry.
 --
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 Mr. Susi Lehtola, PhD             Research Associate
 susi.lehtola.++.alumni.helsinki.fi   Department of Applied Physics
 http://www.helsinki.fi/~jzlehtol  Aalto University
                                   Finland
 ---------------------------------------------------------------
 Susi Lehtola, FT                  Tutkijatohtori
 susi.lehtola.++.alumni.helsinki.fi   Fysiikan laitos
 http://www.helsinki.fi/~jzlehtol  Aalto-yliopisto
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