Computational methods Critical

This last definition should be carefully appHed as either an interpolation or an extrapolation, particularly for empirical computational methods based on diverse observations. It is critical that users of molecular modeling tools understand where it is appropriate to apply a technique and where it is not, and what degree of accuracy can be expected. 

In the context of drug discovery, computational methods do not add value unless they can achieve practical results. Results must be produced quickly enough so that they can influence decision making in chemical synthesis. Most importantly, computational methods must be accurate enough to maintain the trust of the medicinal chemist. Without this trust, computational predictions will rarely be tested in the laboratory, which will then prevent the generation of critical data useful for improving the original predictions. 

The tautomerism of furoxan (l,2,5-oxadiazole-2-oxide) has been investigated by different computational methods comprising modern density functions as well as single-reference and multi-reference ab initio methods. The ring-opening process to 1,2-dinitrosoethylene is the most critical step of the reaction and cannot be treated reliably by low-level computations (Scheme 2). The existence of cis-cis-trans- 1,2-dinitrosoethylene as a stable intermediate is advocated by perturbational methods, but high-level coupled-cluster calculations identify this as an artifact <2001JA7326>. 

Calculation Methods for Critical Loads of Heavy Metals The selection of a computation method or model is the third step in the flowchart for calculating critical loads of heavy metals (Figure 4). There are different models that can be used to calculate critical loads for terrestrial and aquatic ecosystems, based on receptor properties and on certain critical limits. Relevant aspects in relation to the selection of a calculation method are... 

The study described above for the water-gas shift reaction employed computational methods that could be used for other synthesis gas operations. The critical point calculation procedure of Heidemann and Khalil (14) proved to be adaptable to the mixtures involved. In the case of one reaction, it was possible to find conditions under which a critical mixture was at chemical reaction equilibrium by using a one dimensional Newton-Raphson procedures along the critical line defined by varying reaction extents. In the case of more than one independent chemical reaction, a Newton-Raphson procedure in the several reaction extents would be a candidate as an approach to satisfying the several equilibrium constant equations, (25). 

Computational chemistry offers many advantages to teachers of physical chemistry. It can help students learn the material and develop critical thinking skills. As noted before, most students will probably use some sort of computational method in their chemistry careers, so it provides students with important experience. Furthermore, computational chemistry is much more accessible to undergraduate students than it was a decade ago. Desktop computers now have sufficient resources to calculate the properties of illustrative and interesting chemical systems. Computational software is also becoming more affordable. Students can now use computers to help them visualize and understand many aspects of physical chemistry. However, physical chemistry is also an experimental science, and computational models are still judged against experimental results. 

Incorporation of computational methods will be a critical feature of the undergraduate education of future chemistry students. Computational methods have become ubiquitous in large part because they enhance the dynamic understanding of molecular systems. Scientists are able to develop a level of insight and intuition not easily obtained from experiments or equations alone. It is vitally important that students understand the fundamental methods, learn to think critically about specific approximations and methods employed, and develop the ability and incentive to evaluate carefiilly the results obtained from... 

Theory and experimental methods. Since the combined experimental-theoretical approach is stressed, both the underlying theoretical and experimental aspects receive considerable attention in chapters 2 and 3. Computational methods are presented in order to introduce the nomenclature, discuss the input into the models, and the other approximations used. Thereafter, a brief survey of possible surface science experimental techniques is provided, with a critical view towards the application of these techniques to studies of conjugated polymer surfaces and interfaces. Next, some of the relevant details of the most common, and singly most useful, measurement employed in the studies of polymer surfaces and interfaces, photoelectron spectroscopy, are pointed out, to provide the reader with a familiarity of certain concepts used in data interpretation in the Examples chapter (chapter 7). Finally, the use of the output of the computational modelling in interpreting experimental electronic and chemical structural data, the combined experimental-theoretical approach, is illustrated. 

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