Computational quantum chemistry isolated molecule

Computational quantum chemistry has been used in many ways in the chemical industry. The simplest of such calculations is for an isolated molecule this provides information on the equilibrium molecular geometry, electronic energy, and vibrational frequencies of a molecule. From such information the dissociation energy at 0 K is obtained, and using ideal gas statistical mechanics, the entropy and other thermodynamic properties at other temperatures in the ideal gas state can be computed. Such calculations have provided information on heats of formation of compounds and, when used with transition state theory, on reaction pathways and reaction selectivity. As these applications are well documented in the literature, they are not discussed here. 

The idea that molecular structure is related to a compound s bulk properties is inherent to chemistry. For example, a compound containing a carboxylic group is acidic. This concept leads to a fundamental tenet of computational chemistry structure-property relationships exist and may be quantified. A natural step is to inquire about using first principles (quantum mechanics) to calculate an appropriate property such as a pK value, for example. Quantum mechanical (QM) calculations involving isolated molecules are practical however, QM calculations for systems involving collections of molecules, such as would be required for pK values, are very time consuming. 

To conclude, we hope that readers will share with us the feeling that ASC methods treating solvent effects open the possibility to introduce a large part of the quantum chemistry methods in the realm of solutions, with a computational cost comparable with that needed for isolated molecules. We also think that this report shows that PCM h a structure flexible enough to allow many other modifications, improvements and extensions. To do it a... 

Ab initio quantum chemistry has now achieved such a level of maturity that it can satisfactorily predict most properties of isolated, relatively small molecules from a theoretical point of view. One now attempts to apply the theory to more complicated and expensive experimental observations. However, there is an even greater need for the computer simulation of solids to be equally predictive. Good corre-... 

The relationship between molecular structure and chemical reactivity does not need to be emphazised, and the success of quantum chemistry in computing the electronic properties of a molecule is well established nowadays. Nevertheless it is worth recalling that quantum chemical techniques deal with small molecular systems which are either isolated or which undergo a well defined external perturbation. As soon as one extends the concept of individual molecules to a liquid, one is faced with quite a different situation, in which the modifications introduced by the liquid surroundings on the molecular structure may be far from negligible. 

With the powerful quantum mechanical computational methods that are presently available, it is possible to obtain accurate at initio electronic wavefunctions for modest to large size systems. The availability of powerful computers, especially workstations, and vector and massively parallel supercomputers, makes it possible to take extensive advantage of these computational methods. The recent advances in both computer architecture and numerical methods have been truly breathtaking and we are now able to obtain reasonably accurate solutions for isolated molecules as well as for cluster models of condensed matter. In this review, our concern is for the use of cluster models to describe chemistry at solid surfaces in particular, the chemical bond formed between adsorbates and solid substrates. 

Standard quantum chemical computations are performed on a single molecule or complex. This isolated species represents a molecule in the gas phase. While gas-phase chemistry comprises an important chemical subdiscipline, the vast majority of chemical reactions occur in solution. Perhaps most critical is that aU of biochemistry takes place in an aqueous environment, and so if computational chemistry is to be relevant for biochemical apphcations, treatment of the solvent is imperative. 

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