Molecular orbital methods electron distribution from

Between the wall of the cell and any ions (H+, H30+, H502+) forces of supermolecular hydrogen P-bonds and electrostatic y-bonds operate (see Fig. 2). Surfaces of intermolecular potential energy have been calculated by density functional method stated in our paper [6], Necessary data about spatial distributions of electron charge density inside framework of aqua multiparticle had been taken from calculations of aquatic ions and the ring of water (H20)n by using of standard molecular orbital method in the minimal basis set (STO-3G). Results of calculations are shown in Table 1. 

The ground-state wave function of cytosine has been calculated by practically all the semiempirical as well as nonempirical methods. Here, we shall discuss the application of these methods to interpret the experimental quantities that can. be calculated from the molecular orbitals of cytosines and are related to the distribution of electron densities in the molecules. The simplest v-HMO method yielded a great mass of useful information concerning the structure and the properties of biological molecules including cytosines. The reader is referred to the book1 Quantum Biochemistry for the application of this method to interpret the physicochemical properties of biomolecules. Here we will restrict our attention to the results of the v-SCF MO and the all-valence or all-electron treatments of cytosines. 

The detailed study of electron distribution rearrangements in a chemical reaction needs a multiconfiguration ab initio method, because one determinantal wavefunctions are unreliable away from equilibrium geometries. By means of the CASSCF method it is possible to focus attention on the electrons more directly involved in the reaction, allowing the calculation to be done with a relatively limited number of Slater determinants. Moreover, CASSCF uses orthogonal orbitals which are simpler than non-orthogonal orbitals in the development of computer codes. Nowadays CASSCF is, in fact, efficiently included in practically all distributed packages for molecular quantum calculations. 

There are other shortcomings in semiempirical TDDFT that are not related to the self interaction. Semiempirical TDDFT has the same overall formalism and algorithmic structure as TDHF and the energy distribution of excited-state roots from these methods is much less dense than the exact distribution from FCI. In other words, while TDDFT is formally an exact theory for excited states (cf. Runge-Gross theorem [2]), semiempirical TDDFT has only one-electron excitations just as TDHF or CIS, which are the crudest approximations in excited-state molecular orbital theory. 

The hyperfine structure constant thus allows us to probe the electron distribution in radicals. Theoretically calculated values of the spin densities can then be compared with the experimental values obtained from Eq. (9). One of the simplest methods for calculating electron density in an aromatic hydrocarbon is to use Hiickel molecular orbital theory as discussed later. 

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