Second Challenge Overview

Objective of the Challenge

A commonly held future vision of molecular simulation is that it becomes a so-called "breakthrough" technology [1]. By this we mean a technology that takes us significantly beyond the current methods to new levels of efficiency, accuracy, and applicable regimes of molecular types and state conditions. As an outgrowth of the Workshop on Predicting the Thermophysical Properties of Fluids by Molecular Simulation held at NIST in 2001, an objective of this simulation challenge is to encourage the development of scientifically-based potentials for use in molecular simulations. This has been recognized as a barrier to wide acceptance and implementation of molecular simulation in industry [1].
Definition of Molecular Simulations
By definition, a molecular simulation is any method that involves an ensemble of many molecules whose coordinates are "evolved in accordance with a rigorous calculation of intermolecular energies or forces" [2]. Consequently, only entries that are consistent with this definition of a molecular simulation will be considered for the awards in this molecular simulation challenge.
Comparison with Other State-of-the-Art Methods
The challenge aims to evaluate the current capabilities of molecular simulations and provide a forum for comparing them with other state-of-the-art prediction methods (e.g., group contribution, equation of state, methods based on statistical thermodynamics, quantum chemistry, etc.) for solving problems of industrial relevance. Practitioners of all scientifically-valid methodologies are strongly encouraged to submit entries in order to demonstrate the applicability of the methods in accordance with the general constraints of the contest. All outstanding entries will be considered for inclusion in the IFPSC session at the AIChE annual meeting and associated journal issue. However, only methods conforming to the definition of molecular simulations given in section 2 will be in the running for the awards in the simulation challenge. This is intended to leave the door open to a variety of computational approaches while maintaining the primary focus on molecular simulations. Novel approaches to these problems are particularly desired.
Objectives for Problem Selection and Evaluation
In many cases, reliable experimental data are available at near ambient conditions but are sparse, conflicting, or non-existent at elevated temperatures and/or pressures. Measurements under those conditions may also be difficult or expensive to perform in the laboratory. Therefore, the ability to quantitatively predict these properties at elevated temperatures and/or pressures given near-ambient data would be very useful in an industrial setting.
Though the generality and transferability of a method and force field are also desirable, these concerns are often secondary to requirements for the quantitative accuracy of the data. This is especially true for a method (such as molecular simulation) whose accuracy for a given molecule or mixture of molecules and a given property is difficult to predict a priori without extensive practical experience (which motivates one of the objectives of this competition; namely, to serve as a benchmark of what level of accuracy can be reasonably expected if the correct answer for the problem is not known ahead of time). Thus, in an industrial setting, it would not be advisable to ignore commonly available data for a given molecule in order to develop a method or force field that is more general but is not sufficiently accurate for the molecule(s) and property of interest. For this reason, the committee has chosen to continue to place the primary emphasis of the competition on quantitative accuracy rather than generality or other measures of merit. The restrictions on the use of experimental data have been chosen in an attempt to reflect the common industrial experience that reliable data are often available for pure fluids and/or ambient conditions but not for mixtures and/or high temperatures and pressures.
Requirements for Entry Submission
A submission for any one of the problem sets is to be in the form of a manuscript suitable for submission to a refereed, archival, open-literature journal. The manuscript must contain sufficient detail about the simulation method and about the force field so that an experienced simulator could reproduce the results without requiring access to proprietary information. In particular, all potential parameters and molecule geometry parameters must be explicitly specified in the manuscript. The results are to be reported in SI units.
An analysis of the uncertainty in the calculated results is required. This information will be considered in the initial screening of the entries (see the final paragraph below). The uncertainty in the benchmark experimental measurements will also be quantified. Predictions that fall within the estimates of the experimental uncertainty will be treated as being in exact agreement with the experiment (i.e., 0 % deviation).
In addition, the manuscript must be consistent with the specific requirements and restrictions for the individual problem set. Any force-field parameters (published or unpublished) may be used as long as they do not violate the restrictions of the individual problem sets regarding what data my be used and are reported in the manuscript submitted to the contest committee.  Any force-field parameters published in a peer-reviewed journal by the date of the Contest announcement may be used, regardless of what experimental data were used to derive them. Note that this supersedes the restrictions set for any of the individual problem sets.
In order to facilitate the double-blind judging of the entries, the title page (with the authors' names) and the list of references/citations should be provided on separate sheets from the body of the manuscript. (Specific references will be provided to the judges if requested.) Any page headers/footers should not identify the authors or their institutions. If acknowledgements are needed, they should also be on a separate sheet. If entrants choose to enter more than one of the competitions, separate entries should be prepared.
It is also expected that the participants in this competition will develop or apply force fields and methodologies that can model a variety of chemistries and materials in different states (e.g. liquid and vapor) with levels of precision, accuracy, and computational efficiency that are comparable to other similar work published in the peer-reviewed scientific journals of the field. Entries are expected to present results that are statistically significant and to present sufficient supporting evidence to establish this quality. Also, the scientific reasoning behind any new (unpublished) force field parameterizations must be clearly spelled out in the entry. If there is a consensus among the judges that an entry is of poor quality (e.g., uses a method commonly accepted to be fundamentally flawed, presents results that are not statistically significant, fails to provide sufficient supporting data and details, violates the various rules and guidelines established for the competition, or for any other reason would be unlikely to be accepted by any peer-reviewed scientific journal in the field), that entry will be rejected and will not be considered in the judging.
How to Submit Entries
Potential entrants, interested observers, and those willing to help in the judging process are requested to register.
Though the contest committee would prefer that potential entrants register earlier rather than later, registration may be completed at any time prior to submitting to an entry (registration is a prerequisite for entry submission).
Manuscripts must be submitted no later than Friday, September 10, 2004, to Raymond Mountain, competition chair, in either paper or electronic form.
Address paper submissions to: 
Raymond Mountain 
National Institute of Standards and Technology 
100 Bureau Drive Stop 8380 
Gaithersburg, MD 20899-8380 USA
Send electronic submissions in pdf format only to: 
Manuscripts received prior to August 27, 2004 will be examined for consistency with the contest rules and feedback will be provided to the authors 1 week before the September 10, 2004 deadline.
1. "Chemical Industry of the Future, Technology Roadmap for Computational Chemistry", Tyler Thompson, ed., 1999, 
2. R.J. Sadus, Molecular Simulation of Fluids, Elsevier, 2002
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