How many modelers?

March 8th, 2010 by Gerhard Goldbeck-Wood, PhD

How many of “us” are out there? I mean how many people doing modeling and simulation? I’d really like to know, ideally broken down by discipline, such as Materials Science vs Life Science, and quantum, classical and mesoscale.

Alas, there are preciously few statistics on that, so when I read in the Monthly Update (Feb 2010) of the Psi-k network that they conducted a study on size of the ab initio simulation community, it got my immediate attention.

Representing a network of people from the quantum mechanics field, Peter Dederichs, Volker Heine and colleagues Phivos Mavropoulos and Dirk Tunger from Research Center Jülich searched publications by keywords such as ‘ab initio’, and made sure not to double-count authors. In fact they tend to underestimate by assuming people with the same surname and first initial are the same. As Prof Dederichs, the chair of the network tells me, checks were also made to ensure that papers from completely different fields are not included. Also they estimate that their keyword range underestimates the number of papers by about 10%. Of course there are those that didn’t publish a paper in 2008, the year for which the study was done. Moreover, Dederichs says, there are those who published papers which don’t have proper keywords like “ab initio” or “first principles” in the abstract or title, so they are not found in the search. All of that is likely to compensate for counting co-authors that are not actually modelers.

All in all, they come up with about 23,000 people! And the number of publications in the field indicates a linear rise year on year.

That’s quite a lot more than they expected, and I agree. The global distribution was also surprising, with about 11,000 in Europe, about 5,600 in America, and 5,700 in East Asia (China, Japan, Korea, Taiwan and Singapore). That’s a lot of QM guys, especially here in Europe. Now, there will be a response from the US on that one I guess?

I wonder how many classical modelers there are. I’d hazard a guess that the number of classical modelers is about half those in the QM community, at least in the Materials Science field. Assuming that the mesoscale modeling community is quite small, that would make for a total of at least 30,000 modelers worldwide.

What is your view, or informed opinion? Anybody else knows about or has done some studies? I am going to open up a poll in the right sidebar on the number of people involved in quantum, classical and mesoscale modeling in total. It would be great to hear also how you came up with your selection.

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Spectroscopy: Where Theory Meets the Real World

February 23rd, 2010 by George Fitzgerald, PhD

One of the most successful uses of quantum mechanical modeling methods is to predict spectra. These methods are capable of yielding good predictions of UV/Visible, NMR, Infrared, Raman, THz, and EELS (electron energy loss spectroscopy) to name just a few. Spectroscopy (according to Wikipedia) is the “study of the interaction between radiation and matter as a function of wavelength … or frequency.” How does this help chemists? We can use the spectra to determine the structure of new molecules or materials; to determine the composition of mixtures; or to follow the course of a chemical reaction in situ. How does modeling help with this? In a number of ways, but I’ll cover just 2.

One way modeling comes into play is by working with experimental results to remove ambiguities. When a chemist is trying the determine the structure of a new material, he or she takes a spectrum, or two, or three. His or her knowledge of the ingredients together with the spectra gives a pretty good idea what the chemical or crystal structure is. In a lot of cases the data are sufficient only  to narrow this down to 3-4 possible structures. Molecular modeling resolve this ambiguity by predicting the spectrum of each possibility; the spectrum that matches the experimental one presumably corresponds to the “right” one. Modeling is even more valuable when investigating defect structures like this work on Mg2.5VMoO8.

Another use is telling where experimentalists to look for the spectral peaks of a new compound. This can be especially important when trying to detect the spectra of new, novel, or poorly characterized materials. Experimental terahertz (THz) spectroscopy, for example, examines the spectral range of 3-120 cm-1, and can be used for detection and identification for a wide assortment of compounds including explosives like HMX. It’s a lot safer to investigate these materials by modeling than in the lab.

A recent blog by Dr. Damian Allishighlights the importance of doing the simulations correctly. (By the way, Damian, congrats on getting to page 1000.) A lot of work for the past 40-odd years has gone into predicting spectra of isolated – or gas phase – molecules. But materials like HMX are crystalline, and calculations on the isolated molecules make for poor comparison with crystals. The recent work underscores how important it is to simulate crystals using crystals. And it’s not just for THz spectra. Recent work on NMR leads to the same conclusion. A couple of programs can do this. Damian’s blog focuses on DMol3 and Crystal06, but we should also mention CASTEP and Gaussian as other applications capable of predicting a wide variety of properties for solids.

Let’s keep modeling – but be careful out there: short cuts will lead to poor results, and molecular modeling will end up taking the rap for user error.

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DFT Redux

January 14th, 2010 by George Fitzgerald, PhD

I thought I’d start the year with an easy blog, simply following up on my earlier ramblings of 25 October 2009: DFT Goes (Even More) Mainstream. In that article I discussed the success of Density FunctionalTheory (DFT) and used the annual number of publications as a metric. The numbers show that publications grew by over 25% per annum, but the results for 2009 were naturally incomplete.

Happily the trend continued through 2009 for a total of 4621 DFT references in ACS Journals. Here are a few of my favorite publications, thought not all are drawn from the ACS citations. Yes, of course, these use Accelrys DFT packages, but they are still pretty cool articles:

Let me and my readers know what you think are the most interesting DFT articles from 2009.

†Strictly speaking, this was not QSAR, Quantitative Structure-Activity Relationship, because they didn’t actually base predictions on the structure. I use the term here more generally to refer to relationships that predict complex properites like catalytic activity, on the basis of simpler properties, like workfunction.

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Materials Studio 5.0: A particle-ular challenge

December 11th, 2009 by Stephen Todd, PhD

In the last of the series of my blogs on Materials Studio 5.0 functionality, I will be writing about new functionality in the mesoscale area. Back in Materials Studio 4.4, we developed a new module called Mesocite. Mesocite is a module for doing coarse-grained molecular dynamics where the elementary particle is a bead. In coarse-grained molecular dynamics, a bead typically represents several heavy atoms. This has advantages over classical molecular dynamics such as Forcite Plus as you can access longer time and length scales.

In Materials Studio 5.0, we added the capability to do Dissipative Particle Dynamics (DPD) to Mesocite. DPD is a very coarse-grained dynamics approach where the bead can represent many atoms or even molecules. We already have a module which can do DPD in Materials Studio but this has limited ability to be extended. By developing the new DPD in Mesocite, we could take advantage of the underlying MatServer environment to easily extend DPD to run in parallel and work with MaterialsScript amongst other things.

One issue we faced is that the legacy DPD tool works in reduced units whereas MatServer requires physical units. The use of reduced units is fairly standard in DPD however it makes it more difficult to relate the results back to experimentalists. Therefore, we thought that switching to physical units would be a good idea. However, there were still questions as to how customers would work with a DPD in physical units. We asked a small focus group of customers very early in the release as to how they would like to parameterize DPD calculations. All agreed that getting the results in physical units was preferable but they still wanted to set up the calculations in reduced units as they have lots of historical data they want to re-use. So, we have a new user interface which allows setup in either reduced or physical units but then converts to physical units for the calculation!

When a new piece of functionality is added to Materials Studio, I like to add a tutorial on how to apply the software, what sort of values customers should use, and how to get the most out of the software. For the new DPD functionality, I looked at several papers before settling on an application by Groot and Rabone looking at the effect of non-ionic surfactants on membrane properties. This interested me as it demonstrates the strength of mesoscale in looking at varying concentrations of different components and seeing the effect on morphology. I also realized that I could use some of the Mesocite analysis to really analyze the system for properties such as concentration profiles and examining the diffusivity of the beads across the membrane. This mapped really well to the original results and produced what I hope is an interesting tutorial.

There was another reason I chose this paper too – Groot and Rabone also looked at the effect of strain on the membrane. This wasn’t possible with the old DPD module but, using some MaterialsScript, I could strain the system and then calculate the surface tension. As I like to dabble with MaterialsScript, the lure of this was irresistible and the script I made is available from the Accelrys Community website.

One minor issue was that the system sizes and relative amounts were not clear from the paper. Luckily there are several ex-Unilever people at Accelrys, so one of my colleagues, Dr Neil Spenley, contacted one of the authors, Dr Robert D. Groot. I was also lucky that Dr Groot obviously hordes his old research work and, a day later, I had the original DPD input file in my hands!

The results from the strain calculations also show the same trends as those reported by Groot and Rabone so I was pretty happy with this work.

So that wraps up my blogs on Materials Studio 5.0. I hope to have given you an insight into some of the processes that go into making a new version of Materials Studio.

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So long AIChe and Tennessee

November 12th, 2009 by Michael Doyle, PhD

The show was excellent and we saw many people; old friends and new, young users of modeling tools. The level of interest, in a range of approaches, from chemical process development to solar energy and bio mass, point to an exciting future and the opportunities that may occur as we face the challenges of the next decade and beyond.

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Headin’ to AIChE…

November 9th, 2009 by Michael Doyle, PhD

Sat here in my seat en-route to the 2009 AICHE meeting, although a weekend flight, I had plenty of time to catch up on the back issues of my journals. So it was with interest I read Derek Lowe’s column on Pharmaceutical production and formulation as well as Anne Thayer’s on sustainable chemical synthesis and Rick Mullins in Process IT. I wonder how these themes of better formulation design, greener synthesis and better reaction solvent use, and linking process chemistry into business decision making will be reflected in the talks over the next 4 days.

The location sounds very exciting and – I am shocked to say after traveling on business to 45 countries, its my first time in Nashville. I am excited and hope to have some excellent discussions with scientists and engineers.

This meeting is a mile stone for those of us in the modeling and simulation area, since we are now releasing Materials Studio 50 which represents over 15 years continuous development and which on a simple PC platform encompasses quantum, atomistic, meso and data scale simulations.

There is as I say above many challenges in chemistry now perhaps more than ever, and I am certain these tools have a growing place in the chemists tool set when facing them and a growing applicability across all areas of science and materials development.

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In search of a lead – one fragment at a time!

July 21st, 2009 by Accelrys Team

The quest to find novel lead compounds is still the same, but the computational paradigms tend to shift. It is evident from the recent scientific conferences and publications that fragment based design (FBD) is a popular method in finding novel compounds against biological targets of interest.

FBD is predominantly an experimental approach whereby research groups are using well established techniques, such as NMR and X-ray crystallography, for finding small molecules that bind to proteins.

It wasn’t until recently that computational approaches started to take on the buzzword, or perhaps some of the computational methods were ahead of their times! Such is the case with an algorithm called “Multiple Copy Simultaneous Search” or MCSS. A popular request came via our Discovery Studio (DS) users to see this algorithm from InsightII environment into a more user friendly DS.

It was in 1991 that Martin Karplus and co-workers at Harvard University had first published this force-field based method and demonstrated its used in fragment-based design. Since then, MCSS has been successfully applied by several research groups in generating ideas and suggesting binding modes of small molecules. Why the MCSS name? The algorithm takes a small molecule fragment, makes hundreds of copies of it, and then simultaneously minimizes them in the receptor cavity. Fragments with favorable binding energy are ranked for analysis.  Efficient and clever.

So, by popular demand, we have developed an enhanced MCSS algorithm in Discovery Studio 2.5, which promises to help chemists and modelers in their search of a lead compound – one fragment at a time.

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