State-and property-specific approach

Abstract The basic argument of the state- and property-specific approach (SPSA) to... 

This chapter reviews the main characteristics of a state- and property-specific approach (SPSA) to quantum chemistry as developed and implemented since the early 1970s by the author and collaborators. I discuss several examples and, in addition, 1 point to key elements of the background from the 1960s. 

Because there is a central theme that pervades the formalisms and applications of this work, its framework has been given the generic name of The state-specific approach (SSA) (Nicolaides, int. J. Quantum Chem. 60, (1996) 119 ibid, 71, (1999) 209). According to the SSA, critical to the development of formalism which is physically helpful as well as computationally practical is, first, the choice of appropriate for each problem forms of the trial wavefunctions and, second, the possibility of employing corresponding function spaces that are as specific and optimal as possible for the state and property of interest. A salient feature of the SSA is that it makes the interplay between electronic structure and dynamics transparent. 

Returning to multilayer adsorption, the potential model appears to be fundamentally correct. It accounts for the empirical fact that systems at the same value of / rin P/F ) are in essentially corresponding states, and that the multilayer approaches bulk liquid in properties as P approaches F. However, the specific treatments must be regarded as still somewhat primitive. The various proposed functions for U r) can only be rather approximate. Even the general-appearing Eq. XVn-79 cannot be correct, since it does not allow for structural perturbations that make the film different from bulk liquid. Such perturbations should in general be present and must be present in the case of liquids that do not spread on the adsorbent (Section X-7). The last term of Eq. XVII-80, while reasonable, represents at best a semiempirical attempt to take structural perturbation into account. 

Linear response function approaches were introduced into the chemistry literature about thirty years ago Ref. [1,2]. At that time they were referred to as Green functions or propagator approaches. Soon after the introduction it became apparent that they offered a viable and attractive alternative to the state specific approaches for obtaining molecular properties as excitation energies, transition moments and second order molecular properties. 

Both kinetic and thermodynamic approaches have been used to measure and explain the abrupt change in properties as a polymer changes from a glassy to a leathery state. These involve the coefficient of expansion, the compressibility, the index of refraction, and the specific heat values. In the thermodynamic approach used by Gibbs and DiMarzio, the process is considered to be related to conformational entropy changes with temperature and is related to a second-order transition. There is also an abrupt change from the solid crystalline to the liquid state at the first-order transition or melting point Tm. 

There is no doubt that liquid systems represent the majority of chemical work and that all biochemical processes require solvent water for their functionality. At the same time it is clear that the liquid state with a density like a solid but a mobility comparable to the gas phase is the most difficult one for theory. Although classical model systems based on electrostatic and van der Waals forces can provide some insight into the physicochemical behavior of liquids and solutions, specific properties of species formed in a pure liquid or by a solute with the solvent require a more sophisticated approach, which is often attempted by quantum mechanical (QM) calculations of model systems. Such model calculations supply information, however, for an isolated system in the gas... 

The article covers synthesis, structure and properties of thermotropic liquid-crystalline (LC) polymers with mesogenic side groups. Approaches towards the synthesis of such systems and the conditions for their realization in the LC state are presented, as well as the data revealing the relationship between the molecular structure of an LC polymer and the type of mesophase formed. Specific features of thermotropic LC polymers and copolymers of nematic, smectic and cholesteric types are considered. 

The last fundamental aspect characterizing PCM methods, i.e. their quantum mechanical formulation, is presented by Cammi for molecular systems in their ground electronic states and by Mennucci for electronically excited states. In both contributions, particular attention is devoted to the specific aspect characterizing PCM (and similar) approaches, namely the necessity to introduce an effective nonlinear Hamiltonian which describes the solute under the effect of the interactions with its environment and determines how these interactions affect the solute electronic wavefunction and properties. 

The simple harmonic terms used to represent the energy of bond stretching in typical protein molecular mechanics force fields cannot model the making and breaking of chemical bonds. Also, molecular mechanics parameters are usually developed based on the properties of stable molecules, and so might not be applicable to transition states and intermediates. Molecular mechanics functions and parameters can be developed specifically for reactions, an approach that has been... 

The current state of knowledge does not permit a correlation between structure and function though correlations between structural stability and surfactant properties of proteins has been developed (14). Because of side chains of component amino acids and their involvement in non-covalent interactions markedly influence structure and function of proteins, the chemical modification of specific reactive groups should facilitate alteration of functional properties. This approach, though empirical at present, may also provide useful information concerning the role of specific amino acid groups in conformation and functionality of protein. 

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