me? from New Jersey. living in Austin, Texas. registered Democrat, so it's hard living here :) married, no kids. came here for graduate school in 1991, ended up with a master's in geology and a ph.d. in chemistry (theoretical chemical physics). tried to hang in academia (2 postdoc's, UCSF and Princeton), ended up doing machine learning for high-frequency algorithmic trading for a few years. now, doing python-related scientific software dev, which really mostly is web stuff
ok, can I use 6-31g basis set with m06-2x functional to get single point energy between a hydrogen bonded pair (keeping in mind Hbonds are highly directional) ? @Todd
so what's the point ? If I plot the whole set of points I'm getting then the curve pattern should be same but the magnitude of energy will only vary. @PH13
i would think you should go with the most complete basis set (as @PH13 says) and make sure that whatever level of theory you use, include polarization functions (dunno re: diffuse for your system)
if it takes months you should be very sure what you are doing
the longest run I took was somewhat around 900 hrs (opt+freq) ... and that was because I used a basis set that was too huge for my system ... I regret doing this
I don't know it in detail so I cannot say anything about it. And even if I'd know more about I wouldn't say something about it because I still have so much to learn ^^
the key factor I have to deal with is directionality in case of H-bonds, and which is mainly because of charge transfer component of this kind of bonds. So, if I used m06-2x functional wouldn't it be possible to get the correct energy ?
as m06 suit of functions deals with charge transfer component very precisely, as per most recent literature.
and the "correct" energy with dft is such a thing. as per theory dft is variational which means you cannot go deeper than the true energy. but as what we do is not dft but dfa and the functionals we use are somewhat empirical this variational stuff doesn't count and as with mp2 you can result in a lower energy than the true energy ... so be cautious about the "correct" energy ... whatever this is
Cough cough clears voice: Ahem, I hereby declare your arrest according to code 13 in correlation of violation of bacteria rights code 0XFFF3362 of the United Nations' database. You are under arrest, sir, and anything you say might be used against you as balloons in the court. Guards, seize him.
@PH13 Riiight, I was thinking about it earlier yesterday. . .