The ever increasing power of modern computers and the continuing evolutions/revolutions in approaches to solving the very basic equations of quantum and statistical mechanics is rapidly establishing computation and simulation as a primary tool for discovery, innovation, and optimization of materials and processes. In the area of nano-technology, the necessity to understand at the level of quantum mechanics the systems we seek to create and measure makes use of these tools inescapable. This project seeks to establish the validity, limits of applicability, and quantitative measures of uncertainty for the large array of software tools being employed by industry and academia. Joint planning with industry is a core element in the planning for efforts in both simulation of fluid properties and creation of tools for nano-science. Current and future tasks within this project include: �Computational Chemistry Comparison Benchmark Data Base CCCBDB�, �Applied Computational Chemistry � fluid-solid interface and nano-mechanics�, �Reactivity � pathways, rates, energetics�, �Computational Nano-science�, and �Quantum Biochemistry and Physics�.

• Systematic Validation and Improvement of Quantum Chemistry Methods for the Prediction of Physical and Chemical Properties Assessing the Accuracy and Reliability of Density Functional Theory: Density Functional Theory (DFT) has become one of the most widely used quantum chemistry methods mainly due to its relatively low computational expense. In this project researchers have performed a systematic validation of a particular family of DFT functionals, the so-called �hybrid-GGA�, in order to assess their accuracy and transferability to different chemical properties. This study showed marked erratic behavior leading to the conclusion that these functionals are not transferable to the computation of different chemical properties. In addition, the results of this work indicate that the major source of error can be traced back to the so called �exchange� functional. In order to solve the problems exhibited by the �exchange� functionals we developed a rigorous and efficient method (the SC-a method) for the calculation of the exact �exchange� functional. This method has been implemented in various popular quantum chemistry software packages and it has been tested in more than 40 molecules and the results have shown the possibility of computing the exact �exchange� functional in complicated polyatomic systems at the computational cost comparable to the inexpensive Hartree-Fock formalism. Encouraged by these results, researches focused on procedures that could improve the �exchange-correlation� functional as a whole and have developed a general and simple methodology called the �Approximate Self-Consistent Potential� (ASCP). The method has been implemented in two of the most popular quantum chemistry packages and tested in the calculations of absolute energies and atomization energies of 20 different molecules. The results indicate that the method is robust and sufficiently general. .
• Theory of Non-Bonded Interactions: Molecular Association and Assembly: Fundamentals of van der Waals Interactions in Aromatic Clusters . The molecular systems ideally suited for a detailed study of intermolecular potentials are van der Waals (vdW) dimers and higher clusters of aromatic hydrocarbons formed as a direct consequence of intermolecular interactions. Overall, the results obtained in this project indicate that the combination of molecular dynamics simulations using the MM3 force field, followed by full geometry optimizations at the MP2/6-31G level of theory appear to provide a reliable tool for the study of van der Waals aromatic clusters. Given that the study of larger vdW clusters involving more than four aromatic molecules is almost impossible even at the MP2/6-31G level, researchers have performed a systematic comparison of the results obtained with the very efficient Hartree-Fock Dispersion (HFD) methodology they previously developed and the results computed at the MP2/6-31G level of theory. It was found that HFD predicts structures and binding energies in very good agreement with the much more costly MP2/6-31G method.
• Prediction of Mixture Phase Behavior Using Transition-Matrix Monte Carlo Simulation: The fluid-phase behavior of mixtures is a subject of immense industrial and technical importance. Building upon recently developed transition-matrix Monte Carlo methods, we have developed a new simulation methodology (see references 6 and 7 below) capable of precisely predicting an entire isothermal fluid-phase diagram in a single simulation in a significantly shorter amount of CPU time relative to existing methods. To validate the mixture transition-matrix Monte Carlo method (M-TMMC), we have investigated a number of binary mixtures whose phase behavior is well known, and also mixtures that are known to pose problems for conventional methods. M-TMMC produced results in excellent agreement with literature data in all cases. Additionally, we found that the relative uncertainties of the predictions were at most 0.2%, an order of magnitude improvement over current methods.
• Computational Chemistry Illuminates Atomistic Processes at Complex Interfaces: The hematite (0001) surface, a -Fe 2 O 3 , is important for many reasons.  It is the catalytic surface used commercially to convert ethyl benzene to styrene, the most prevalent mineral surface exposed to ground and surface water, and is a model surface to study corrosion for ferrous-based metals. With the integration of experiment and theory we have successfully identified the surface chemistry that characterizes the fundamental interactions of iron and aluminum oxides with oxygen and water, two of the most prevalent and reactive species in the environment.

• Gonzalez I. ; Gonzalez C. ; Karasiev VV.; Ludena E.; Hernandez A.; "Basis Set Dependent SC Alpha Exchange-Only and Exchange-Correlation Calculations" J. Chem. Phys . 118 , 8161 , 2003.
• Irikura, K. K.; Johnson, R. D., III; Kacker, R. N. Metrologia 41 , 369-375 , 2004.
• Gonzalez , C.A. , and Lim, E.C.; �Hartree-Fock Dispersion (HFD) Study of the Equilibrium Structures of Small Microclusters of Benzene: Comparison with MP2 Geometries �; J. Phys. Chem. A. 105 , 10583-10587, (2001).
• Gonzalez , C.A . , and Lim, E.C., �On the Equilibrium Geometries of Anthracene Trimer and Naphthalene Tetramer: Comparison of the Exp 6-1 Potential and HFD Structure Predictions with Experiment,� Chem. Phys. Lett . 357 , 161 (2002)
• Gonzalez C ., Lim E., �Evaluation of the Hartree-Fock dispersion (HFD) model as a practical tool for probing intermolecular potentials of small aromatic clusters: Comparison of the HFD and MP2 intermolecular Potentials,� J. Phys. Chem. A 107 , 10105, (2003).
• V. K. Shen and J. R. Errington, The Journal of Physical Chemistry B , (in press).
• V. K. Shen and J. R. Errington, The Journal of Chemical Physics ,(in press).
• Wang, X.-G., Chaka, A.M., Scheffler, M., Phys. Rev. Lett. 84 , 3650 (2000).
• C. Lemire, S. Bertarione , A. Zechina, D. Scarano, A,M. Chaka, S.Shaikhutdinov, and H.-J. Freund , Phys. Rev. Lett. Submitted.
• Thomas P. Trainor, Anne M. Chaka, Peter J. Eng, Matt Newville, Glenn A. Waychunas, Jeffrey G. Catalano, Gordon E. Brown, Jr, Surface Science 573 , 204-224 (2004).