Supermolecule approach

On one hand, there are the dielectric properties, which are especially important for polai solvents like water. Bulk properties can, on the other hand, only be modeled by using a supermolecule approach with explicitly defined solvent molecules. 

Resonance energies and tautomerism of substituted aromatic heterocycles and their benzo derivatives Reaction-field-supermolecule approach to calculation of solvent effects... 

The simplest discrete approach is the solvaton method 65) which calculates above all the electrostatic interaction between the molecule and the solvent. The solvent is represented by a Active molecule built up from so-called solvatones. The most sophisticated discrete model is the supermolecule approach 661 in which the solvent molecules are included in the quantum chemical calculation as individual molecules. Here, information about the structure of the solvent cage and about the specific interactions between solvent and solute can be obtained. But this approach is connected with a great effort, because a lot of optimizations of geometry with ab initio calculations should be completed 67). A very simple supermolecule (CH3+ + 2 solvent molecules) was calculated with a semiempirical method in Ref.15). 

The continuum models represent a real alternative to the supermolecule approach. In this cases the solvation energy Esolv is assumed to be a sum of individual terms which can be calculated separately (see Eq. (6)). 

The basis set used for calculations were the STO-3G, the 3-21G, and the 6-31G basis sets, as implemented by the Gaussian-88 computer program. The energies of interaction were computed by using the supermolecule approach where the sum of the energies of the subsystems are substracted from the energy of the complex. All the species were geometry optimized. 

The alternative theoretical scheme for studying chemical reactivity in solution, the supermolecule approach, allows for the investigation of the solvation phenomena at a microscopic level. However, it does not enable the characterization of long-range bulk solvent forces moreover, the number of solvent molecules required to properly represent bulk solvation for a given solute can be so large that to perform a quantum chemical calculation in such a system becomes prohibitively expensive. ... 

The supermolecule approach was able to rationalize changes in the ligand-binding affinities for the 5-HT1A-R. The good linear correlations obtained through the Vin and Vdif indexes... 

A very similar QSAR approach for the modeling and prediction of selectivity of oq-AR antagonists has recently been carried out by Eric el al. It confirms the usefulness of the supermolecules approach and of the ad hoc shape descriptors in the rationalization of cq-ARs affinity and cq-AR subtype selectivity [98]. 

De Benedetti, P.G., Fanelli, F., Menziani, M.C. and Cocchi, M. (2000) The ad hoc supermolecule approach to receptor ligand design. Journal of Molecular Structure (Theochem), 503, 1-16. 

Cocchi, M. and De Benedetti, P.G. (1998) Use of the supermolecule approach to derive molecular similarity descriptors for QSAR analysis. Journal of Molecular Modelling, 4, 113-131. 

Other than MRCI calculations with relatively few electrons (say six or fewer), methods that do not even try to achieve correct scaling are unlikely to prove satisfactory. Even a Davidson-type correction is preferable to nothing at all. CPF/MCPF and especially CCSD/QCISD should be strongly preferred over CISD. And unless an exactly size-consistent method is being used, fragment energies should be computed using a supermolecule approach. 

One point to address concerns the use of the words s pramolecular and supermolecule. The concept of supramolecular chemistry has become a unifying attractor, in which areas that have developed independently have spontaneously found their place. The word supramolecular has been used in particular for large multiprotein architectures and organized molecular assemblies [1.16]. On the other hand, in theoretical chemistry, the computational procedure that treats molecular associations such as the water dimer as a single entity is termed the supermolecule approach [1.34,1.35]. Taking into account the existence and the independent uses of these two words, one may then propose that supramolecular chemistry be the broader term, concerning the chemistry of all types of supramolecular entities from the well-defined supermolecules to extended, more or less organized, polymolecular associations. The term super molecular chemistry would be restricted to the specific chemistry of the supermolecules themselves. 

Specific solute-solvent interactions, such as hydrogen bonding or protonation, may be included in the calculation of the shielding of solute nuclei by a supermolecule approach. The appropriate structure of the solute-solvent supermolecule may be obtained by the use of molecular mechanics simulations. At the semi-empirical MO level this approach has been successfully used to describe the effects of hydrogen bonding on the nuclear shielding of small molecules. 

Space does not permit the inclusion of any of the papers dealing with hydrogen bonding188 or solvation phenomena,189 and the reader is referred to the above references for more details. It is clear, however, from recent work that it is feasible to include the interaction with several solvent molecules using the supermolecule approach, and very interesting and informative results have been obtained in this way. 

Interaction energies (Eim) on the basis of ab initio calculations are in general evaluated according to the so-called supermolecule approach ... 

The discussion of the preceding paragraphs clearly shows that indeed supermolecule method should be applied with great care. So we wish to end this section by saying that even though the supermolecule approach is conceptually very simple it cannot be used by simply running standard black box programs of quantum chemistry. 

Quantum Chemical Approaches to Modelling Enzyme Reactions Cluster (or Supermolecule) Approaches... 

In the second family of approaches, explicit solvent molecules are placed around the gas phase stationary point structures. In some cases, the gas phase geometries are held constant and only the geometries and/or positions of the surrounding solvent molecules are optimized, and in other cases, the structure of the whole system (often called a supermolecule 32) is optimized. The supermolecule approach generally only involves explicit solvent molecules from the first (and occasionally second) solvation shell of the solute. 

It is also possible to combine the supermolecule and continuum approaches by using specific solvent molecules to capture the short-range effects (i.e., those involving specific noncovalent interactions between solute and solvent) and a reaction field to treat longer range effects.33-35 Alternatively, structures along the gas phase reaction coordinate can be immersed in a box of hundreds (or more) of explicit solvent molecules that are treated using force field approaches.36,37 Each type of method - the SCRF, solvent box, and supermolecule approaches - tests the importance of particular features of the solvent on the reactivity of the solute dielectric constant, multiple specific classical electrostatic interactions, and specific local directional noncovalent interactions, respectively. 

---