Ceilidh ... Re^4: , Intermolecular effects on electron density

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Re^4: , Intermolecular effects on electron density

Thanks for the advice. Yes, many people have recommended me NBO. In Gamess, I would need to recompile the code with NBO support (in case I obtain a license). This is an advantage of Firefly. Unfortunately, I do not have much time to play with al these programs right now.

On Fri Jan 16 '09 4:18pm, Slawomir Janicki wrote
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>The analysis method depends on the goals and the target audience. I happen to like NBO more because it provides a picture (or actually, many pictures) in terms of bonds, antibonds, and lone pairs. These are easier to understand for a organic chemist at the bench (like me and my customers).

>I can't help you with the cost decision. However, your project looks like a self-supported academic research, so perhaps you could appeal for a free limited use license to Frank Weinhold or Eric Glendening personally. They are both very human :) and easy to talk to.
>
>
>On Fri Jan 16 '09 1:03am, Miro Moman wrote
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>>On Fri Jan 16 '09 0:20am, sanya wrote
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>>>>I have already carried out a geometry optimisation of the system at
>>>>the HF/6-31+G(2d,p) level of theory using Gamess (freezing the
>>>>coordinates of 3 atoms to prevent significant changes in the relative
>>>>orientation of the two molecules).

>>>I'd better use DFT (say, B3LYP or PBE0) for this system. Its computational cost is almost the same as HF, but the electron correlation is included in the functional and, therefore, you'll get better geometries. Alternatively, you may use MP2, but it is a bit more expensive.

>>Thanks for the advice. Indeed, I am using B3LYP/6-311++G(2d,2p) to do a Hessian type of calculation with the optimised geometries. But I could not get the geometry optimisation to converge at this level of theory because it was taking too long (I am running the calculations on my personal laptop, this is a collaboration which is unrelated to my current research). Interestingly, I could not get the geometry to converge at a any level of theory below HF/6-31+G(2d,p) either.

>>Now the question is which method would be more reliable to do the electron density analysis. Gamess outputs the Mulliken and Löwdin population analyses, but the results are slightly contradictory and maybe not very meaningful in this case. Another option would be NBO, but it is not free and I think it is not worthy for my to buy a license for just this particular project. Reading the Gamess manual, I came across the Stone's distributed multipole analysis (DMA), but I could not find detailed information on how to tune the several options.

>>Suggestions would be appreciated.

Fri Jan 16 '09 6:44pm

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