Now enjoying the benefits of dispersion-corrected solid-state density functional theory (and a proper MPICH2 implementation for infrared intensity calculations, although this now a problem for reasons to be addressed in an upcoming post) in Crystal09, three issues in recent calculations caused me to think hard enough about keyword formats and job runs that I have opted to post briefly about what to do in case google and bing are your preferred methods of manual searching.

1. How To Run Only A Single-Point Energy Calculation In Crystal06/Crystal09

This had never come up before and, by the time I needed to find an input file to see what do to, the first google search provided Civalleri’s Total Energy Calculation page that currently has broken links to .zip files. There is quite a bit about the different geometry optimization approaches in the manual, but a search for “single-point” provides no information about what to do for only single-point energy calculations.

The solution, it should be obvious after, is simply to not include the geometry optimization section in the input file. What would otherwise be the following (with arbitrary geometry optimization-like info between [COORDINATES] and [BASIS SETS]…

[COORDINATES]
OPTGEOM
TOLDEG
0.000005
TOLDEX
0.000020
END
END
[BASIS SETS]

becomes…

[COORDINATES]
[BASIS SETS]

One problem solved by simply not having any optimization parameters (again, makes sense and is now google-able).

2. Proper GRIMME Input Format For Long-Range Dispersion Contributions In Crystal09

This is another example where one’s first efforts in translating the manual into calculations may lead to considerable confusion until the proper format is finally identified (by which time you’ve run many pruned-down input tests).

GRIMME
1.05 20. 25.
1.05 20. 25. s6 (scaling factor) d (steepness) Rcut (cutoff radius)
5
1  0.14 1.001 Hydrogen Conventional Atomic number , C6 , Rvdw
6  1.75 1.452 Carbon Conventional Atomic number , C6 , Rvdw
7  1.23 1.397 Nitrogen Conventional Atomic number , C6 , Rvdw
8  0.70 1.342 Oxygen Conventional Atomic number , C6 , Rvdw
17 5.07 1.639 Chlorine Conventional Atomic number , C6 ,'Rvdw

I’m not even sure where the final ,’Rvdw comes from. Your .out file may terminate with the following error (or something similar)…

rank 7 in job 8  korterquad_51438   caused collective abort of all ranks
  exit status of rank 7: killed by signal 9

And the ERROR.peN file with any content will show the following, clearly pointing to a GRIMME-specific error…

 ERROR **** GRIMME_INPUT **** ELEMENT NOT DEFINED:           1

The problem is the additional content within the manual pages for the GRIMME keyword that require pruning (or, at least, some identifier to show what is and what is not needed). The proper GRIMME section above is properly provided in the INPUT file as…

GRIMME
1.05 20. 25.
5
1  0.14 1.001
6  1.75 1.452
7  1.23 1.397
8  0.70 1.342
17 5.07 1.639

Where (see page 88 of the Crystal09 manual)…

GRIMME <- keyword is called
1.05 20. 25. <- scaling factor, steepness, cutoff distance
5 <- number of elements in the list (not the total number of atoms)
1  0.14 1.001 <- atomic number, dispersion coefficient, van der Waals radius
...

When all is properly run, the bottom of your output file will look something like the following:

 CYC  43 ETOT(AU) -5.784662098123E+03 DETOT  1.18E-11 tst  8.17E-15 PX  6.73E-08

 == SCF ENDED - CONVERGENCE ON ENERGY      E(AU) -5.7846620981229E+03 CYCLES  43

 ENERGY EXPRESSION=HARTREE+FOCK EXCH*0.20000+(BECKE  EXCH)*0.80000+LYP    CORR

 TOTAL ENERGY(DFT)(AU)( 43) -5.7846620981229E+03 DE 1.2E-11 tester 8.2E-15
 TTTTTTTTTTTTTTTTTTTTTTTTTTTTTT EDFT        TELAPSE     4705.82 TCPU     4651.41

 *******************************************************************************

 GRIMME DISPERSION ENERGY CORRECTION

 SCALE FACTOR (S6):     1.0500

 GRIMME DISPERSION ENERGY (AU) -1.9723347118951E-01
 TOTAL ENERGY + DISP (AU) -5.7848593315941E+03

 *******************************************************************************

The Crystal09 manual refers you to Table 1 of the Stefan Grimme paper, “Semiempirical GGA-type density functional constructed with a long-range dispersion correction” (Journal of Computational Chemistry, Volume 27, Issue 15, Pages 1787 – 1799), which I’ve put together into the proper format below. Be sure to (1) delete the elements in parentheses ( -> get rid of the (H) <- ), (2) remove those atoms you do not need, (3) be sure to change the “number of elements” number for your structure, and (4) get and reference the Grimme paper so you have the proper C6 parameters and van der Waals radii accounted for (you’ll be the right nitwit if I mis-copied something and you ran with it (although I trust my input), and you should have the reference regardless).

( H)   1   0.14 1.001
(Li)   3   1.61 0.825
(Na)  11   5.71 1.144
( K)  19  10.80 1.485
(Rb)  37  24.67 1.628

(Be)   4   1.61 1.408
(Mg)  12   5.71 1.364
(Ca)  20  10.80 1.474
(Sr)  38  24.67 1.606

( B)   5   3.13 1.485
(Al)  13  10.79 1.639
(Ga)  31  16.99 1.650
(In)  49  37.32 1.672

( C)   6   1.75 1.452
(Si)  14   9.23 1.716
(Ge)  32  17.10 1.727
(Sn)  50  38.71 1.804

( N)   7   1.23 1.397
( P)  15   7.84 1.705
(As)  33  16.37 1.760
(Sb)  51  38.44 1.881

( O)   8   0.70 1.342
( S)  16   5.57 1.683
(Se)  34  12.64 1.771
(Te)  52  31.74 1.892

( F)   9   0.75 1.287
(Cl)  17   5.07 1.639
(Br)  35  12.47 1.749
( I)  53  31.50 1.892

(He)   2   0.08 1.012
(Ne)  10   0.63 1.243
(Ar)  18   4.61 1.595
(Kr)  36  12.01 1.727
(Xe)  54  29.99 1.881
Y-Cd      24.67 1.639
Sc-Zn     10.80 1.562

Note that the d-block is identical for each row (so no atom numbers provided).

3. Removing The MPICH2 Content From The Output File In Pcrystal(/09)

This final issue does not occur in Pcrystal(/06) but does in Pcrystal(/09), with the reason being (I assume) the new use of MPICH2 in Pcrystal(/09) instead of MPICH in Pcrystal(/06).  The problem comes from running the following set of commands at the terminal window in MPICH2:

mpiexec -machinefile machine -np N /path/to/Pcrystal &>FILENAME.out &

Embedded within the FILENAME.out file will be all flavors of MPI-specific output, perhaps such as the following (in this case errors, but it happens in proper output as well):

application called MPI_Abort(MPI_COMM_WORLD, 1) - process 4
application called MPI_Abort(MPI_COMM_WORLD, 1) - process 7
rank 7 in job 9  korterquad_51438   caused collective abort of all ranks
 exit status of rank 7: return code 1
rank 4 in job 9  korterquad_51438   caused collective abort of all ranks
 exit status of rank 4: killed by signal 9

or…

mpiexec_machine (handle_stdin_input 1089): stdin problem; if pgm is run in background...
mpiexec_machine (handle_stdin_input 1090):     e.g.: mpiexec -n 4 a.out < /dev/null &

The solution is to break up the mpiexec output from the Pcrystal output, performed by directing the mpiexec-specific content to, in this case, /dev/null (because it is not necessary except for diagnostic purposes).

mpiexec -machinefile machine -np N /path/to/Pcrystal < /dev/null &>FILENAME.out &

Which removes all traces of mpi-specific output from FILENAME.out.

The cover art for the 7 May 2010 issue of the Journal of Organic Chemistry accompanies the article by (2nd semester organic chemistry professor, co-author, and 2010 American Chemical Society James Flack Norris Award in Physical Organic Chemistry recipient) John E. Baldwin and Alexey P. Kostikov entitled “On the Stereochemical Characteristic of the Thermal Reactions of Vinylcyclobutane.”

This Perspective outlines the stereochemical and mechanistic complexities inherent in the thermal reactions converting vinylcyclobutane to cyclohexene, butadiene, and ethylene. The structural isomerization and the fragmentation processes seem, at first sight, to be obvious and simple. When considered more carefully and investigated with the aid of deuterium-labeled stereochemically well-defined vinylcyclobutane derivatives there emerges a complex kinetic situation traced by 56 structure-to-structure transformations and 12 independent kinetic parameters. Experimental determinations of stereochemical details of stereomutations and [1,3] carbon sigmatropic shifts are now being pursued and will in time contribute to gaining relevant evidence casting light on the reaction dynamics involved as flexible short-lived diradical intermediates trace the paths leading from one d2-labeled vinylcyclobutane starting material to a mixture of 16 structures.

The cover image is meant to convey as much useful information as possible without any verbiage, although this is clearly not a concept meant to be crystal clear to a non-chemist (but kudos if you got the idea without my having to address it).

Included below are the four iterations involved in the cover draft, between which a considerable amount of verbal back-and-forth occurred (that is discussed briefly) to get what was intended to be presented. The iterations are provided both to show how different visions of what might be seen as the most-key of the key points change as content is presented to the client/researcher and, frankly, these all involved quite a bit of busy work and it seems a shame to not have them floating around somewhere accessible.

The original cover idea (above) was quite mundane but provided a bit more information (cryptic as it may appear to the non-mechanistic organic chemist) about what might be occurring in the absence of a brief read of the introduction of the article. This image emphasizes that a constant rearrangement occurs of the vinylcyclobutane (by the many, many arrows and the four different arrangements of deuteriums in the rearrangement) but does not address that the other 12 structures are products of reactions that are generated as the vinylcyclobutane rearranges and undergoes other but simultaneous intramolecular reactions. The absence of the connection between the rearrangement and the formation of products (which include the vinylcyclobutanes) removed this first iteration from the final running.

The second iteration (above) is a significant (well, I think so) improvement in the getting-across of the business end of the research. The vinylcyclobutane rearrangement is still central to the preferred emphasis of the cover (soon to go away) and the connection between the rearrangement and the formation of products is now hinted at directly by the use of the faded arrows. The second-tier information passed along in this image is that the vinylcyclobutane is one of the products, which is not stressed in the image (by the inclusion of four additional arrows from the central graphic (and, with that addition, the inclusion of arrows feeding the vinylcyclobutanes back into the center). If this had been an Angew. Chemie article, the circular design would have been a perfect fit.

It was at this point that a new piece of content was provided in the form of a medium-resolution digital photo of a piece of artwork by Anne Baldwin. The artwork was chosen as much for the colors as for the chaotic quality of the swirls, which was the one aspect of the entire process that the previous two images did not address and which Dr. Baldwin saw as the more significant point to convey. Some Gaussian blurring and a Gaussian basis set later, the new reactant/product combination as scrambled to complement the background and to make clear that one molecule (that at the arrow) lead to everything else in the image, including itself. The slight red halo around the deuterium (dark blue) is a result of an overlay of the blue spheres and red spheres rendered with slightly larger radii.

The arrow color and shading was stolen from Jean-Michel Folon. Example (The Cry) below. If you’ve one of the copies of La morte di un albero (mine is #630), see Comme un aimant (1971).

I admittedly prefer this (that is, the above cover idea) to the final version as the arrow indicates the forward direction of reactions and adds a hint of symmetry to an otherwise jumbled image.

As for the selected cover image (and final iteration, above), the considerable real estate taken up by the vinylcyclobutane in the previous image is recovered, which highlights the starting molecule differently and has the arrow simply angled into a less-busy space.

The final selection may make more sense in light of the image Baldwin chose to use for the graphical abstract.

A word to the perspective cover artist – This is a point that should be obvious but is often not until it is made obvious by an editor when it is much too late. Your images should be as LARGE as possible. Each of the images above is a 200 MB Photoshop file that would print without pixilation or granularity at 600 dpi on a 24” x 36” poster.

Accepted in the Journal of Physical Chemistry A, with my fingers crossed for pulling off the rare double-header in an upcoming print edition of the journal (having missed it by three intermediate articles with the Cs₂B₁₂H₁₂ and HMX papers back in 2006 (you’d keep track, too). A fortuitous overlap of scheduled defense dates between P. Hakey, Ph.D. and M. Hudson, A.B.D.). A brief summary of interesting points from this study is provided below, including what I think is a useful point about how to most easily interpret AND represent solid-state vibrational spectra for publications.

An alternate view of molecular vibrational motion comes from considering not the contents of the defined unit cell but the hydrogen-bonding and ionic bonding arrangement that exists between pairs of molecules between unit cells. The colorized image below shows two distinct chains (red and blue) that, when the predicted vibrational modes are animated, become trivial to characterize as the relative motions of a hydrogen/ionic-bonded chain. Rotational motions appear as spinning motions of the chains, translational motions as either chain sliding motions or chain breathing modes. It appears as a larger macromolecule undergoing very “molecular” vibrations. In optical vibrational spectroscopy, selection rules and the unit cell arrangement do not produce in- and out-of-phase motions of the red and blue chains, as only one “chain” exists in the periodicity of the unit cell. In neutron scattering spectroscopy, these relative motions between red and blue would appear in the phonon region. This same discussion was had, in part, in a previous post on the solid-state terahertz assignment of ephedrine (with a nicer picture).

So, look at the cell contents, then see if there’s more structure than crystal packing would indicate. It greatly simplifies the assignment (which, in turn. greatly simplifies the reader’s digestion of the vibrational motions).

Patrick M. Hakey, Damian G. Allis, Matthew R. Hudson, Wayne Ouellette, and Timothy M. Korter

Department of Chemistry, Syracuse University, Syracuse, New York 13244-4100

Abstract: The terahertz (THz) spectrum of (S)-(+)-ketamine hydrochloride has been investigated from 10 to 100 cm^-1 (0.3-3.0 THz) at both liquid-nitrogen (78 K) and room (294 K) temperatures. Complete solid-state density functional theory structural analyses and normal-mode analyses are performed using a single hybrid density functional (B3LYP) and three generalized gradient approximation density functionals (BLYP, PBE, PW91). An assignment of the eight features present in the well-resolved cryogenic spectrum is provided based upon solid-state predictions at a PW91/6-31G(d,p) level of theory. The simulations predict that a total of 13 infrared- active vibrational modes contribute to the THz spectrum with 26.4% of the spectral intensity originating from external lattice vibrations.

pubs.acs.org/journal/jpcafh
www.somewhereville.com/?p=29
www.somewhereville.com/?p=26
www.somewhereville.com/?p=126
en.wikipedia.org/wiki/Density_functional_theory
en.wikipedia.org/wiki/Ketamine
www.crystal.unito.it
accelrys.com/products/materials-studio/quantum-and-catalysis-software.html
en.wikipedia.org/wiki/Time_domain_terahertz_spectroscopy
en.wikipedia.org/wiki/Computational_chemistry
accelrys.com
en.wikipedia.org/wiki/Inelastic_neutron_scattering
en.wikipedia.org/wiki/Vibrational_spectroscopy
www.somewhereville.com/?p=680

Available as an ASAP in The Journal of Physical Chemistry A. As a general rule in computational chemistry, the smaller the molecule, the harder it is to get right. As a brief summary, parabanic acid has several interesting properties of significance to computational chemists as both a model for other systems containing similar sub-structures and as a complicated little molecule in its own right.

1. The solid-state spectrum requires solid-state modeling. This should be of no surprise (see the figure below for the difference in solid-state (top) and isolated-molecule (bottom)). This task was undertaken with both DMol³ and Crystal06, with DMol³ calculations responsible for the majority of the analysis of this system (as has always been the case in the neutron studies reported on this site).

2. The agreement in the hydrogen-bonded N-H…O vibrations is, starting from the crystal structure, in poor agreement with experiment. You’ll note the region between 750 and 900 cm^-1 is a little too high (and for clarification, the simulated spectrum is in red below). According to the kitchen sink that Matt threw at the structure, the problem is not the same anharmonicity one would acknowledge by Dr. Walnut’s “catalytic handwaving” approach to spectrum assignment (Dr. Walnut does not engage in this behavior, rather endeavors to find it in others where it should not be).

3. The local geometry of the hydrogen-bonding network in this molecular solid leads to notable changes in parabanic acid structure that, in turn, leads to the different behavior of the N-H…O vibrational motions. There is one potentially inflammatory comment in the Conclusions section that results from this identification. The parabanic acid molecule is, at its sub-structure, a set of three constrained peptide linkages that under go subtle but vibrationally-observable changes to their geometry because of crystal packing and intermolecular hydrogen bond formation. This means that the isolated molecule and solid-state forms are different and that peptide groups are influenced by neighboring interactions.

So, why should one care? Suppose one is parameterizing a biomolecular force field (CHARMM, AMBER, GROMOS, etc.) using bond lengths, bond angles, etc., for the amino acid geometry and vibrational data for some aspect of the force constant analysis. The structural data for these force fields often originates with solid-state studies (diffraction results). This means, to those very concerned with structural accuracy, that a geometry we know to be influenced by solid-state interactions is being used as the basis for molecular dynamics calculations that will NOT be used in their solid-state forms. Coupled with the different spectral properties due to intermolecular interactions, the description being used as the basis for the biomolecular force field likely being used in solution (solvent box approaches) is based on data in a phase where the structure and dynamics are altered from their less conformationally-restricted counterpart (in this case, solid-state).

A subtle point, but that’s where applied theoreticians do some of their best work.

It doesn’t happen often.  Simply marking for interested parties that David Bradley wrote a piece about the recent L-Alanine Alaninium Nitrate article published in Physical Chemistry Chemical Physics (Phys. Chem. Chem. Phys., 2009, 11, 9474 – 9483, DOI: 10.1039/b905070a) with a specific focus on the organic ferroelectric behavior of this system as argued from the results of the inelastic neutron scattering (INS) and temperature-dependent Raman spectroscopic studies.  Also, of course, the entire discussion and analysis revolves around the results of the density functional theory (DFT) studies performed on the solid-state system with DMol3.

I find it mildly amusing that a paper that went through several rather exhaustive crystallography-focused review cycles (fighting with crystallography-specific reviewers about the use of the vibrational spectroscopy to provide the more realistic view of this organic salt in the solid-state) makes headlines (well, you know) only for the vibrational spectroscopy.  I certainly won’t point fingers (only browsers), but I’ve yet to see someone say the same of vibrational spectroscopists.

As a brief addition, the Raman spectrum presented on the spectroscopyNOW website does not provide quite the resolution of the original.  In the interest of laying all doubts aside, a larger version of the same image is provided below.

The 293 K and 78 K Raman spectra of LAAN showing temperature-dependent peak changes (black box).

According to the article (his, not ours)…

Even if there turns out to be no ferroelectric transition in LAAN, it could still represent an unusual and intriguing structure in which both a neutral and zwitterionic L-alanine amino acid exist in the same crystal cell together with crystalline nitric acid. Such a material might help to improve the computational structural models, improve our understanding of the spectra of related materials and perhaps offer clues to designing a next-generation material that does have the elusive ferroelectric properties.

The article is available at www.spectroscopynow.com/coi/cda/detail.cda?id=22458&type=Feature&chId=3&page=1.  A local copy of the article (in PDF format) is here: 2009december1_spectroscopynow_organicferroelectrics.pdf

www.spectroscopynow.com/coi/cda/detail.cda?id=567&type=Feature&chId=0&page=1
www.somewhereville.com/?p=775
www.rsc.org/publishing/journals/cp/Index.asp
www.rsc.org/publishing/journals/CP/article.asp?doi=b905070a
en.wikipedia.org/wiki/Ferroelectricity
en.wikipedia.org/wiki/Neutron_scattering
en.wikipedia.org/wiki/Raman_spectroscopy
en.wikipedia.org/wiki/Density_functional_theory
accelrys.com/products/materials-studio/modules/dmol3.html
books.google.com/books?id=eZxreAojmj8C&pg=PA19&lpg=PA19&dq=crystallographers+are+bad+scientists&…&f=false
www.spectroscopynow.com
www.spectroscopynow.com/coi/cda/detail.cda?id=22458&type=Feature&chId=3&page=1
www.somewhereville.com/blogfiles/2009december1_spectroscopynow_organicferroelectrics.pdf