Progress toward chemical accuracy in the computer simulation of condensed phase reactions.

We describe a procedure for the generation of chemically accurate computer-simulation models to study chemical reactions in the condensed phase. The process involves (i) the use of a coupled semiempirical quantum and classical molecular mechanics method to represent solutes and solvent, respectively; (ii) the optimization of semiempirical quantum mechanics (QM) parameters to produce a computationally efficient and chemically accurate QM model; (iii) the calibration of a quantum/classical microsolvation model using ab initio quantum theory; and (iv) the use of statistical mechanical principles and methods to simulate, on massively parallel computers, the thermodynamic properties of chemical reactions in aqueous solution. The utility of this process is demonstrated by the calculation of the enthalpy of reaction in vacuum and free energy change in aqueous solution for a proton transfer involving methanol, methoxide, imidazole, and imidazolium, which are functional groups involved with proton transfers in many biochemical systems. An optimized semiempirical QM model is produced, which results in the calculation of heats of formation of the above chemical species to within 1.0 kcal/mol (1 kcal = 4.18 kJ) of experimental values. The use of the calibrated QM and microsolvation QM/MM (molecular mechanics) models for the simulation of a proton transfer in aqueous solution gives a calculated free energy that is within 1.0 kcal/mol (12.2 calculated vs. 12.8 experimental) of a value estimated from experimental pKa values of the reacting species.

GE models and algorithms for condensed phase equilibrium data regression in ternary systems: limitations and proposals

Phase equilibrium data regression is an unavoidable task necessary to obtain the appropriate values for any model to be used in separation equipment design for chemical process simulation and optimization. The accuracy of this process depends on different factors such as the experimental data quality, the selected model and the calculation algorithm. The present paper summarizes the results and conclusions achieved in our research on the capabilities and limitations of the existing GE models and about strategies that can be included in the correlation algorithms to improve the convergence and avoid inconsistencies. The NRTL model has been selected as a representative local composition model. New capabilities of this model, but also several relevant limitations, have been identified and some examples of the application of a modified NRTL equation have been discussed. Furthermore, a regression algorithm has been developed that allows for the advisable simultaneous regression of all the condensed phase equilibrium regions that are present in ternary systems at constant T and P. It includes specific strategies designed to avoid some of the pitfalls frequently found in commercial regression tools for phase equilibrium calculations. Most of the proposed strategies are based on the geometrical interpretation of the lowest common tangent plane equilibrium criterion, which allows an unambiguous comprehension of the behavior of the mixtures. The paper aims to show all the work as a whole in order to reveal the necessary efforts that must be devoted to overcome the difficulties that still exist in the phase equilibrium data regression problem.

History of the city of Denver, Arapahoe County, and Colorado : containing a history of the state of Colorado ... a condensed sketch of Arapahoe County ... a history of the city of Denver ... biographical sketches ...

The historical portion of this work is by W.B. Vickers--Cf. Pref.

Condensed milk and milk powder; prepared for factory, school and laboratory.

Advertising matter: p. 663-696.

Condensed milk and milk powder; prepared for factory, school and laboratory.

Pages 505-560, advertising matter.

The secret of a long and active life and how to enjoy it ... presenting the condensed views, advices and counsel of qualified biologists, physicians, dieticians and specialists, consulted;

On cover: By Frank Linden.

Slavic languages; condensed survey.

Mode of access: Internet.

Twenty lessons in domestic science : a condensed home study course : marketing, food principals, functions of food, methods of cooking, glossary of usual culinary terms, pronunciations and definitions, etc. /

Some recipes use liquor as an ingredient.

The theory and practice of tone relations : a condensed course of harmony designed for the New England Conservatory of Music, Boston, Mass /

Mode of access: Internet.

Income account statements and condensed balance sheets.

St. Louis, & San Francisco Railroad Company, Chicago & Eastern Illinois Railroad Company, Evansville & Terre Haute Railroad Company, St. Louis, Kansas City and Colorado Railroad Company, Arkansas Southern Railroad Company, Chicago & Alton Railroad Company.

Seeing South America; routes, rates, cities, climate, wonders and other condensed information for prospective travelers.

"By William A. Reid."--p. 3.

Seeing South America, condensed facts for prospective travelers.

Mode of access: Internet.

Political annals of Canada: a condensed record of governments from the time of Samuel de Champlain in 1608 down to the time of Earl Grey in 1905: with appendices containing a copy of the British North America Act, establishing the Dominion in 1867: also a list of the first members of the Dominion and provincial parliaments under confederation, and a table of important Canadian historical events,

Mode of access: Internet.

Missouri River basin condensed tabulation of river mileage and drainage areas /

Cover title.

English grammar and business letter writing, condensed and simplified, in three parts.

Mode of access: Internet.