Monthly Archives: June 2011
A new look was needed in this site! and some more changes will be made in the next few days. A new page was added with the topics of the courses I’ve taught here at UAEMex, namely QSAR and Molecular Modeling. Another page was added for you all to leave questions which are hard to fit into other places of this blog. The idea behind this page is just to have a more organized site, since sometimes there are questions on odd places such as the About Me page or something like that.
This blog will slowly transform into a site for my incipient research group, however the blog will always be an important part of this site and will continue to be the front page, at least for now.
Have any comments or suggestions? please let me know in the comments section!
The Natural Bond Orbitals Deletion analysis provides an excellent approach to the assessment of bonding energy within a single molecular fragment or between many. It deletes specific elements of the Fock matrix (this means it sets their values to 0.000) and then re-diagonalizes it in order to find the difference in energy respect to the original matrix. About nine different kinds of deletions are available, which will be briefly summarized in the following section.
One of the main strengths of the NBO derived methods is their almost complete basis set independence, which allows us to obtain comparable numbers under different levels of theory.
Both G03 and G09 use the NBO3.1 program. The 5.0 version is sold separately by their creators, namely prof. Frank Weinhold, who can be contacted through their website. It’s not available for geometry optimizations (gradients),
some people insist on trying to get a different geometry by eliminating a certain interaction and that is just not possible directly with the NBODel method It is indeed possible to perform NBODeletions along with optimizations in G09 (Thanks to prof. Weinhold for his clarifying message) but there are some restrictions: molecular coordinates should be in Z-Matrix format and the number of variables to be optimized should not exceed 50; prof. Weinhold also recommends to use print=0 in the $NBO keylist in order to prevent the output files to become too big. Be sure to start with a proper geometry (close to the desired minimum) since given the nature of this analysis some apretiable geometry effects are to be expected.
The general syntax for its usage includes the string pop=NBODel in the route section of the GaussianX input file. Then, at the end of the file, the following is required:
--End of Input File-- --blank line-- $NBO $END $DEL Interactions to be deleted $END
ENTIRE BLOCKS OF ATOMS
In this kind of deletion one is able to delete all the elements between specific groups of atoms, as if their orbitals (and hence their common Fock elements) did not overlap.
--End of Input File-- --blank line-- $NBO $END $DEL ZERO 2 ATOM BLOCKS 2 BY 3 1 2 3 4 5 3 BY 2 3 4 5 1 2 $END --blank line--
The first line after $DEL indicates how many groups of atoms will be set to zero and the following lines indicate how many atoms belong to each group (i.e. the size of each block which in this case are 2 and 3, respectively). After this line the groups of atoms are listed, in this example all elements from atoms 1 and 2 with those of atoms 3, 4 and 5 will become zero. The next three lines are used for symmetry, so all the interactions from (1,2)->(3,4,5) are deleted along with (3,4,5)->(1,2)
DELETIONS BETWEEN ENTIRE MOLECULAR FRAGMENTS (Intermolecular deletions)
If we want to assess the interaction energy between two molecules, the previous method would consume a lot of time in declaring the size of each block with every atom of each molecule in it, plus there seems to be a limit to the size of the block. In this kind of deletion one is able to delete all the elements between two or more molecular fragments.
--End of Input File-- --blank line-- $NBO $END $DEL ZERO 2 DELOC FROM 1 TO 2 FROM 2 TO 1 $END --blank line--
The delocalizations can also be calculated only in one direction (FROM 1 to 2), in the case above both interactions 1->2 and 2->1 have been deleted. The input for a trimer in which all three fragments interacted with each other would look like this:
ZERO 6 DELOC FROM 1 TO 2 FROM 2 TO 1 FROM 2 TO 3 FROM 3 TO 2 FROM 1 TO 3 FROM 3 TO 1
In short, the number of bilateral delocalizations to be deleted is equal to twice the number of edges in a graph depicting the intermolecular interactions (A post on topology in chemistry is now due).
Reading the output file
Almost at the very end of the output file the following section can be found:
>>>>>>>>>> Convergence criterion not met.
SCF Done: E(RHF) = -4728.57245403 A.U. after 2 cycles
Convg = 0.2354D-03 -V/T = 2.0012
Energy of deletion : -4728.572454034
Total SCF energy : -4728.604640956
Energy change : 0.032187 a.u., 20.198 kcal/mol
The warning about the convergence can be disregarded without any concern about the accuracy of the outcome and it will show in every $DEL calculation. The SCF energy displayed in the second line is the energy corresponding to the modified Fock Matrix, which is the same as the one labeled as Energy of deletion. The Total SCF energy corresponds to the original Fock Matrix; the difference between them is labeled as Energy change and the value is reported in both atomic units as well as kcal/mol.
Some common errors and possible solutions
–> Sometimes you get the following error message at the beginning of the calculation making it crash:
** ERROR IN INITNF. NUMBER OF VARIABLES ( 57) **
** INCORRECT (SHOULD BE BETWEEN 1 AND 50) **
I have found that changing the molecule specification section from Z-matrix to Cartesian coordinates, or vice versa, overcomes this difficulty. Also, if the Opt keyword appears in the route section the previous message will be shown. Opt is
not available under the NBODel method (read the first paragraph for the proper correction).
–> Possible conflicts between NBODel and the usage of DFT methods:
In some revisions of Gaussian 03 there is a conflict when using NBODel and DFT methods. The IOp(5/48=10000) should be included to repair such conflict. This issue was solved in some revision of Gaussian 03 but I don’t know which, so try this if you have problems. Gaussian09 has taken care of the issue although still the usage of DFT to obtain NBODel calculations is not advised.
–> The following error is not self-explanatory:
Error termination via Lnk1e in ‘/../../path’
This particular error arises from the absence of the ‘$NBO $END’ line before the $DEL instruction. The previous line may or may not include additional keywords. If you are interested in computing some kind of deletion energy just leave the line as presented above in all previous examples. My guess is that the $DEL instruction does not calculate the corresponding NBO’s from which to make the deletion but it rather takes all the results from the $NBO instruction and works from there. Bottom line: don’t forget this line!
As with other posts tagged as ‘white papers’, this one will be updated and expanded every time new information is found. In the mean time, thanks to everyone for reading, commenting and rating, this keeps me going with the blog. Have you encountered problems with NBODel methods? share your experiences and solutions with the rest in the comments section.
Have a nice day!
For over twenty years, there has been an ongoing scientific collaboration between the Institute of Chemistry of the National Autonomous University of Mexico and the Faculty of Chemistry and Chemical Engineering of the Babes-Bolyai University located in the city of Cluj-Napoca, Romania. It all began back in the early nineteen nineties when Professor Lara, then director of Instituto de Química, extended an invitation to Professor Ionel Haiduc, who at the time served as Vice President of the Romanian Academy, to spend a few months in Mexico for a research stay. Later on prof. Dr. Ioan Silaghi-Dumitrescu and his wife paid a couple of visits to our institution also during the nineties; their last visit together occurred in 2002 when prof. Ioan Silaghi-Dumitrescu was asked to teach a small course on molecular modelling. It was during this visit that I came to know about the Babes-Bolyai University and more importantly, it was when I met both Prof. Ioan Silaghi and his wife Prof. Luminita Silaghi, an acquaintance that shaped many aspects of my life in the years to come. Other Romanian guests came to work at IQUNAM, such as Dr. Ion Grosu, who worked as a postdoc with Prof. Roberto Martínez in the Organic Synthesis department. Prof. Cristian Silvestru also collaborated with the group of Dr. Raymundo Cea-Olivares in the field of Main Group Metal Chemistry. Prof. Raymundo Cea-Olivares has been to Cluj-Napoca a couple of times visiting the lab of the late Prof. Silaghi. I went for a research stay during my Ph. D. in 2005 and then went back to occupy a postdoctoral position in late 2008 which lasted until 2010; I also participated in the MolMod seminar in 2007 while working at a private research center, then thinking I wouldn’t go back to academia. Dr. Liviu Bolundut, a then Ph. D. student of Prof. Haiduc’s, came to work with Dr. Monica Moya also in the field of Main Group Metal Chemistry. The interaction between our two institutions has a sound history.
As part of the celebrations of this year, the International Year of Chemistry, I issued an invitation to Prof. Ionel Haiduc and Prof. Luminita Silaghi-Dumitrescu, to give a couple of lectures at IQUNAM about their current research. Fortunately, they accepted and found the time in their tight schedules to come. We were also fortunate enough to get the official approval by the corresponding committee at UNESCO of making these conferences part of the official celebrations of IYC 2011 (In fact, they were the ones who came up with the name of the event which is the name of this post as well.) The scope of this visit also included to encourage our scientific community to keep the collaborations alive with UBB. We had these conferences twice, first at CCIQS here in Toluca and also at the original facilities of IQUNAM on the main University campus in Mexico City. Both events were successful in attracting a large number of researchers but more remarkably a large number of young students who have read about their work and are aware of their reputation on their respective fields; the following picture of our guests with young students of UAEMex, serves as proof.
But I get ahead of myself, for in fact we did more than just having lectures and showing them our new facilities. During the course of their stay,which lasted a bit more than a week, Professor Cea-Olivares and I took them around to do some tourism. During their first weekend I took them to the Folkloric Ballet at the Fine Arts Palace and to the Anthropology Museum, both in Mexico City. We also went together to the Aztec ruins of the city center and the larger archaeological site of Teotihuacan, where Mrs. Iovanca Haiduc even got to climb the Sun’s Pyramid, a challenge to which I decided to pass this time. Prof. Cea-Olivares took them outside Mexico City into Cuernavaca and Taxco, the latter being an old silver mining town famous for its jewelry stores filled with Ag merchandise. We all had a great time traveling around, chatting and in general enjoying each others company.
But now back to science. Prof. Haiduc’s lecture was titled “News in Supramolecular Chemistry”, in it he talked about the basics of supramolecular chemistry as the branch of chemistry that deals with the non-covalently bonded chemical species; the chemistry of secondary interactions as defined by Allcock in 1972. A survey of the existing x-ray structures database was performed by Prof. Haiduc along with his colleague Prof. Julio Zukerman-Schpector in Brasil, in order to find some previously overlooked patterns in intermolecular arrays containing Te (II) or Te (IV) along with aromatic groups, revealed that the Te – Ar interactions through the Π electrons cloud are found more often than previously believed. The most remarkable feature of this array is the fact that the electron density in the formation of such interactions stems from the Te atom (through the stereochemically active lone pair) and into the LUMO of the aromatic moiety in the second molecule. This represents a fascinating coordination mode for Te organometallic compounds!
Prof. Luminita Silaghi-Dumitrescu talked about her research on heterotopic As ligands, some of which exhibit remarkable new coordination patterns stabilizing dinuclear complexes with late transition metals. I felt nostalgic reading the names of old friends and colleagues who collaborated in the work described.
Prof. Haiduc (who is currently President of the Romanian Academy) shared many anecdotes about his times as a PhD student at the Lomonosov Institute back in the Soviet Union under the supervision of Prof. Andrianov. From these anecdotes it is possible to extract the feeling of doing science during the Cold War period since he had to be weary of espionage, which by the way went both ways! He talked about secret research facilities and scooped papers. One could easily think that basic chemistry research would be far from the interest of high political powers who could find aeronautical research more interesting! A developed country is able to acknowledge the value of science in preserving a strategic position in the world. His old advisor, Prof. Andrianov, was considered a hero by the Soviet Party among other things for his work on Silicon based polymers which were used as lubricants in heavy machinery and vehicles during War War II. German tanks used regular carbon based oil which in the Russian winter became extremely viscous, practically became gels! while Silicon based oil could almost preserve its original viscosity at very cold temperatures.
In summary it was a great opportunity to learn from great chemists whose scientific reputations could easily overwhelm any scientist worth his salt! But it was above all things a great opportunity to meet once again dear friends from a dear country I once got to call home.
2011 – International Year of Chemistry
“Chemistry – Our life, our future”