Karl,
Thanks for pointing me towards R.E.D.! I've recalculated the partial
atomic charges for 2,3-butanedione with three orientations (REORIENT 1 5 6
| 6 5 1 | 1 6 5) and now get charges very similar to the ones you obtained:
1 C1 -1.901669 0.537275 -0.000004 C 1 BDE
-0.2771
2 H2 -1.894264 1.182435 0.871240 H 1 BDE
0.0869
3 H3 -2.790456 -0.077743 0.000004 H 1 BDE
0.0869
4 H4 -1.894267 1.182414 -0.871265 H 1 BDE
0.0869
5 C5 -0.685377 -0.349477 0.000005 C 1 BDE
0.5252
6 C6 0.685378 0.349478 0.000001 C 1 BDE
0.5252
7 C7 1.901669 -0.537275 -0.000005 C 1 BDE
-0.2771
8 H8 1.894277 -1.182402 0.871265 H 1 BDE
0.0869
9 H9 1.894251 -1.182448 -0.871240 H 1 BDE
0.0869
10 H10 2.790457 0.077740 -0.000031 H 1 BDE
0.0869
11 O11 -0.727342 -1.539145 0.000003 O 1 BDE
-0.5089
12 O12 0.727343 1.539145 0.000003 O 1 BDE
-0.5089
Thanks again!
-ryan
On Wed, Feb 8, 2012 at 8:11 AM, Karl N. Kirschner <
kkirsch.scai.fraunhofer.de> wrote:
> Hi Ryan,
>
> I can basically reproduce your MM results and the Wang et al QM results.
> However, I took a slightly different approach for the quantum calculations
> and the partial atomic charges. Note that due to symmetry, one only needs
> to do a heavy atom rotation from 0-180 degrees (I also did this in 30
> degree increments). I wasn't able to do the single-point calculation at the
> MP4 level, instead I opted for a larger basis set at the MP2 level.
>
> For the QM constraint optimization about the C-C-C-C torsion angle I used
> MP2//6-31++G(d,p). I performed single-point calculations on these
> geometries at MP2/aug-cc-pVDZ (i.e. MP2/aug-cc-pVDZ//MP2//6-31++G(d,p)).
> For partial atomic charges I used R.E.D., with HF/6-31G(d) electrostatic
> potential using the Connolly surface algorithm, and a 2 stage RESP fit
> using weighting factors qwt=.0005/.001. (3 molecular orientations were used
> in the R.E.D. calculations.) All of this was done using GAMESS.
>
> My partial atomic charges are slightly different than yours, but
> ultimately I don't think it matters too much for the internal heavy atom
> rotation of this molecule. Regardless, here are the charges:
>
> 1 C1 -0.7300 0.2420 0.0000 c 1 MOL 0.5239
> 2 C2 0.7300 -0.2420 0.0000 c 1 MOL 0.5239
> 3 C3 1.7980 0.8190 0.0000 c3 1 MOL -0.2739
> 4 H4 1.6930 1.4560 0.8710 hc 1 MOL 0.0861
> 5 H5 1.6930 1.4560 -0.8710 hc 1 MOL 0.0861
> 6 H6 2.7700 0.3460 0.0000 hc 1 MOL 0.0861
> 7 C7 -1.7980 -0.8190 0.0000 c3 1 MOL -0.2739
> 8 H8 -1.6930 -1.4560 0.8710 hc 1 MOL 0.0861
> 9 H9 -1.6930 -1.4560 -0.8710 hc 1 MOL 0.0861
> 10 H10 -2.7700 -0.3460 0.0000 hc 1 MOL 0.0861
> 11 O11 -0.9520 1.4110 -0.0000 o 1 MOL -0.5082
> 12 O12 0.9520 -1.4110 -0.0000 o 1 MOL -0.5082
>
> Attached you can see the resulting potential energy curves. I can
> essentially reproduce the gaff curve and your curve. What I noticed is that
> the resulting molecular mechanics curve is extremely sensitive to the V2
> parameter! By changing the parameter from 1.2 to 2.2 the resulting curve at
> 0 degrees goes from a transition state to a high energy minima.
>
> Concerning the QM calculations, both MP2 calcuations have no local minima
> at 30 degrees, which align well with Wang et al MP4 curve. It is clear that
> the shape of this potential is dependent upon the basis set, and most
> likely the theory level too. I would double check your 30 degree
> conformation (perhaps there is an issue with the improper torsion geometry
> about the ketone functionality).
>
> Concerning the RMSD. I obtain a lower RMSD (averaged over all 7
> conformations, not just the minima) for gaff than for your parameter, which
> is opposite of what you find. For comparison to my MP2//6-31++G(d,p)
> geometries, I obtain an RMSD value of 0.056 for gaff, and 0.058 when using
> your V2.
>
> I don't think this answers your question(s) directly, but I hope that
> helps some :) .
>
> Cheers,
> Karl
>
>
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Received on Fri Feb 10 2012 - 14:30:02 PST
