Category Archives: Internet

Post Calculation Addition of Empirical Dispersion – Fixing interaction energies


Calculation of interaction energies is one of those things people are more concerned with and is also something mostly done wrong. The so called ‘gold standard‘ according to Pavel Hobza for calculating supramolecular interaction energies is the CCSD(T)/CBS level of theory, which is highly impractical for most cases beyond 50 or so light atoms. Basis set extrapolation methods and inclusion of electronic correlation with MP2 methods yield excellent results but they are not nonetheless almost as time consuming as CC. DFT methods in general are terrible and still are the most widely used tools for electronic structure calculations due to their competitive computing times and the wide availability of schemes for including  terms which help describe various kinds of interactions. The most important ingredients needed to get a decent to good interaction energies values calculated with DFT methods are correlation and dispersion. The first part can be recreated by a good correlation functional and the use of empirical dispersion takes care of the latter shortcoming, dramatically improving the results for interaction energies even for lousy functionals such as the infamous B3LYP. The results still wont be of benchmark quality but still the deviations from the gold standard will be shortened significantly, thus becoming more quantitatively reliable.

There is an online tool for calculating and adding the empirical dispersion from Grimme’s group to a calculation which originally lacked it. In the link below you can upload your calculation, select the basis set and functionals employed originally in it, the desired damping model and you get in return the corrected energy through a geometrical-Counterpoise correction and Grimme’s empirical dispersion function, D3, of which I have previously written here.

The gCP-D3 Webservice is located at: http://wwwtc.thch.uni-bonn.de/

The platform is entirely straightforward to use and it works with xyz, turbomole, orca and gaussian output files. The concept is very simple, a both gCP and D3 contributions are computed in the selected basis set and added to the uncorrected DFT (or HF) energy (eq. 1)

eq1 (1)

If you’re trying to calculate interaction energies, remember to perform these corrections for every component in your supramolecular assembly (eq. 2)

eq2(2)

Here’s a screen capture of the outcome after uploading a G09 log file for the simplest of options B3LYP/6-31G(d), a decomposed energy is shown at the left while a 3D interactive Jmol rendering of your molecule is shown at the right. Also, various links to the literature explaining the details of these calculations are available in the top menu.

Figure1

I’m currently writing a book chapter on methods for calculating ineraction energies so expect many more posts like this. A special mention to Dr. Jacinto Sandoval, who is working with us as a postdoc researcher, for bringing this platform to my attention, I was apparently living under a rock.

 

Advertisements

Some Comp.Chem. Tweeps


Out of some +1000 twitter accounts I follow about a quarter are related computational chemistry. The following public list isn’t comprehensive and prone to errors and contains researchers, programmers, students, journals, products and companies who gravitate around the use of in silico methods for the understanding and design of chemical and biochemical compounds.

//platform.twitter.com/widgets.js

I’m putting a new blog out there


As if I didn’t have enough things to do I’m launching a new blog inspired by the #365papers hashtag on Twitter and the naturalproductman.wordpress.com blog. In it I’ll hopefully list, write a femto-review of all the papers I read. This new effort is even more daunting than the actual reading of the huge digital pile of papers I have in my Mendeley To-Be-Read folder, the fattest of them all. The papers therein wont be a comprehensive review of Comp.Chem. must-read papers but rather papers relevant to our lab’s research or curiosity.

Maybe I’ll include some papers brought to my attention by the group and they could do the review. The whole endeavor might flop in a few weeks but I want to give it a shot; we’ll see how it mutates and if it survives or not. So far I haven’t managed to review all papers read but maybe this post will prompt to do so if only to save some face. The domain of the new blog is compchemdigest.wordpress.com but I think it should have included the word MY at the beginning so as to convey the idea that it is only my own biased reading list. Anyway, if you’re interested share it and subscribe, those post will not be publicized.

Virtual Conference in Computational Chemistry VCCC-2014 (1st call)


So many things have happened since I last updated this blog but I will come to write on them when appropriate. Right now I’d like to share an invitation by Prof. Ponnadurai Ramasami from the University of Mauritius to the upcoming Virtual Conference on Computational Chemistry from the 1st to the 31st of August. Deadlines can be consulted here and the most important is the abstract submission on June 30th. This conference is part of the official celebrations of the International Year of Crystallography so talks involving experimental determination of electron densities will be well suited.

I participated in the latest edition and I must say it was a very enriching opportunity to learn from so many other researchers from across the world without leaving my desk. I already know what my talk will be about, now that we are so close to finish and submit a paper on the absence of reactivity for an anti-aromatic set of molecules. (I think I’ll call it “The reactivity of molecules that never existed [but that maybe should have.].) All talks are sent either as pdf, powerpoint presentations, youtube videos, etc. and Q&A are done over e-mail.

So this is a calling to other computational chemists out there who want to participate in this virtual conference. Kudos to Prof. Ponnadurai Ramasami and lets hope we can crystallize his visit to Mexico during 2014 the International Year of Crystallography (pun intended) and here’s to me going sometime to Mauritius!

Negotiations gone wrong and other recent scandals


About a month ago my wife and I got invited by our good friend Dr. Ruperto Fernandez (his PhD is in transport logistics and engineering) to his final presentation for a course in managerial skills he’d taken for over six months, and while I wasn’t all that thrilled about waking up at 8 AM on a Saturday, I went to cheer my good friend and show him my sleepy support. His presentation dealt with negotiations and the required skills to master them, and while he agreed that there is a huge amount of talent involved in being a good negotiator, he also pointed out that some basic knowledge of the procedure can go a long way in helping us with little to no talent in achieving the best possible outcome. Basically, a negotiation involves the agreement between a person with something which another person wants; meeting both parties expectations at the fullest extent possible is the ideal endpoint for an iterative give-and-take between them. Or so it goes.

Recently a scandal that involved the biology freelance blogger DNLee, who blogs for Scientific American with the column The Urban Scientist, took place: DNLee was asked by Biology-Online.org to write for them. Then the negotiation started; she had something the editors wanted: her texts. She agreed to do it and presented her fee (second part of the negotiation process: “I got what you want and here is what I ask in return for it“), instead of having an offer made (third part of the negotiation process: “ok, that is what you want but this is what I can give you“) the blogger got a nasty message, which I believe maybe was intended to elicit a response to better accommodate the editor’s demands but that was nothing more than a plain nasty insult: The editor asked if she was the urban scientist or the urban whore (end of negotiation; nobody got anything. Furthermore, feelings were hurt, reputations questioned and the door for future negotiations between both parties was shut completely). If the editor was unable to pay any fee at all then the editor should have tried to convince the blogger of participating for free; I would have offered her a bigger space than a regular blogger, or maybe even invited her to participate as an editor. I’m not sure they have some sort of business model but something could have been arranged. Had this negotiation not met at any point in the middle then a polite thank you could have left the door open for a future time. DNLee has a reputation that allows her to charge for her writings, had it been me, I’d probably had done it for free but because I need more exposure than her who is already famous. Internet support came promptly and hard as can be seen here and here, not that it wasn’t called for, of course!

But the issue, sadly, didn’t end there, DNLee wrote about this in her blog at SciAm, but the post was later on deleted by the editors. Dr. Mariette DiChristina tweeted that the post wasn’t related to science so it didn’t fit in the site. Pressure in blogs and other social networks prompted SciAm to place the article back on the site. Click here to go to the post.

Calling someone a whore is simply unacceptable.

During his presentation, my friend Dr. Ruperto Fernandez, talked about a negotiation he had with a potential employer. According to his account of the process, it ended quite swiftly when he was offered a much lower salary than the one he currently earns. He said the offer had some good points that could have made him accept even 5 to 10% less income respect to his current salary, but much less than that would not help him cover the bills and that was a total deal-breaker. But the talk didn’t end there, some other joint projects were laid for them to work on together and the door is still open for the future when they may be able to match my friend’s expectations as biology-online should have done with DNLee.

It has been a rough couple of weeks for the Scientific American community; first this and now the leaving of a great science writer, Bora Zivcovic whose misconduct has forced his exit out of the popular magazine. So now the aftermath for both issues remains to be seen. Sexism, though, could be found to be a common denominator in both cases: one was a victim of it, the other one is guilty of inflicting it through various instances of sexual harassment. Should this mean that biology-online, Bora Zivcovic and the affiliated-to-the-two-previous parties, the Scientific American Magazine, are to be deemed as unworthy? I hardly think so. None of us is close to sanctity and we all make mistakes, some of them willingly and other unwillingly but we are accountable for each and every one of them nonetheless; but at the same time we should also be able to separate both sides of each story and keep the best of each side while keeping a close eye (and even a loud mouth) about the wrong in each side.

I wish nothing but the best to every person involved in any of these recent events. Why is it so hard for people to just ‘play nice‘? I’ve heard many times this world would be a better place if we cared more for each other, but sometimes it seems that its actually the opposite; that this world would be be better if we didn’t care so much: if we didn’t care about the color of our skin; our gender; our nationality or ethnicity; our sexual orientation; our social status. This brings me back yet again to that presentation by Dr. Fernandez, where he was asked to describe the way he was perceived by others at his workplace and he said he didn’t quite enjoy social interactions so he is perceived as serious and aloof but was always willing to join a new project, so when reached out for one of these he’s all smiles and work. Shouldn’t we all back off a little bit from each other from time to time?

RealTimeChem week 2013 #RealTimeChem


RealTimeChem, in its first week-long edition, is coming to your Twitter feed next Monday April 22nd 2013, and I for one intend to participate.

I look forward to this event in order to get in touch with other chemists, not only theoretical but experimental ones as well, around the world sharing a passion for chemistry and technology. I guess most of the participants will be experimental chemists who will amaze us with their videos and pictures of cool looking reactions; I hope we, here at our computational lab, are up to the challenge with our calculations.

Participating is really simple, just Tweet as little or as much as you want to share about your work or studies around chemistry under the #RealTimeChem hastag and follow @RealTimeChem. There is also a group and an event set up on Facebook, check those out too. As I write this, its Friday at 8:oo PM and I’m still in the office, which means I have a lot of work to do, therefore I don’t feel like writing about all the details of the event, specially when others have done so in a much more eloquently fashion: Check out these posts (as well as the entire content of their blogs, they’re very cool!) by Dr. Galactic and The Organic Solution for all the details about the event’s mechanics and, yes, even prizes to the best tweets.

So get on board and tweet all week long under the #RealTimeChem hashtag  and share your work with the world the way no journal will ever do: in real time and with the uttermost embarrassing methodology honesty.

%d bloggers like this: