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ORIGINAL POSITIONS OF THE KVANTOVOMEHANICHESKYAPPROACH

The classical chemistry is applicable for the description of properties various veyoshchestv, taken in sufficient volumes for visual supervision whereas at their studying at singlet level the quantum chemistry is used.

The basic partitions of quantum chemistry are: the quantum theory of a structure of molecules, kvanyo
tovaja the theory of chemical bonds and intermolecular interactions, the quantum theory of chemical reactions and reactivity. The problems supplied by these partitions (a structure and properties of molecules and radicals, their reactionary spoyosobnost, etc.) dare methods of quantum mechanics [71, 74, 75, 77].

Properties of atoms and molecules receive at the decision of equation SHredingera intended for particles without a spin and moving much less of a velocity of light, and equation Diraka for relativistic particles with a spin. However analiyoticheskoe the decision of these equations for systems with a considerable quantity of atoms and interreacting electrons is not found till now. The cores settlement meyotody for such connections use model Hartri-Foka-Rutaana (SCF-self consistent field - the self-co-ordinated field, a centre field):

Where Sj - "energy" molecular orbitali i, F μυ - fokian systems, with μυ - koeffiyotsient decomposition molecular orbitali on nuclear orbitaljam (to basic functions - bridging integral:

Here χ - the basic functions aligned on kernels of atoms, r - vectors proyostranstvennyh co-ordinates of electrons.

Model SCF can be improved for not empirical methods inclusion of effects of electronic correlation or considerably to simplify (for poluempiri - cheskih methods), using various approach:

• In Born-Oppengejmera approach wave function of system predyostavljaet itself product of wave function of kernels and wave function of electrons (kernels dvizhutsja it is very sluggish concerning electrons, kotoyorye are taken over for stationary objects);

• In approach Hartri (one-electronic approach) multielectronic wave function is product of one-electronic functions - oryobitalej (electrons move independently from each other);

• In approach MO LKAO (molecular orbital - linear kombinayotsija nuclear orbitalej) functions molecular orbitalej are liyonejnoj a combination of the basic functions aligned on kernels

Where ψ μ - wave function molecular orbitali, χv - basic function.

In kvantovo-chemical calculations these of approach allow to set priyoblizitelnuju structure of a molecule in the form of a set of co-ordinates of kernels, to choose basis - quantity of analytical functions by which will be approximated radiyoalnye parts of backs-orbitalej. Because of increase of complexity of search of decisions rasyotet complexity of set of equations and the requirement to accuracy of calculation that result ins to increase of time and power expenses.

In semiempirical settlement methods a part of integrals of bridging (the equation 1.1.2.) in model Hartri-Foka-Rutaana (1.1.1.) replace empiricheskiyomi with data or equate to zero. The results received with ispolzovaniyoem of this approach, often not only less resursoemki, but also are more exact. Fidelity of calculations is provided with correctness of selection of empirical parametres. OdYOnako parametrization strongly narrows area of their application to one viyoda connections and one-two properties [71, 74, 75, 77]. For kvantovo-chemical calculation in software package Gaussian it is possible to use some procedures of similar type: AM1, PM3, PM6, CNDO, INDO, MINDO/3, MNDO, ZINDO [9].

Neempirichesky, or methods Hartri-Foka [71, 74, 75, 77], are considered naiyobolee exact in quantum chemistry as give the chance to find the decision of wave function without attraction of experimental data [79]. The wave function reflecting approach Hartri:

Result ins to distinction of all particles of system (principle infringement tozhdestvenyonosti). Each electron is numbered by "quantum number", and a pure condition
Molecules it is replaced by product of pure conditions for electrons (system subsystems of the noninteracting among themselves charged bodies make). Each particle interreacts with the "effective" external field created by other particles, and twin interactions are not present. All it brings sushchestvenyonuju an error in the decision of equation SHredingera. Fok has finished method Hartri, having presented asymmetric wave function of a molecule in the form of a determinant. The initial uniform equation has broken up to the equations for each electron, dviyogajushchegosja in somebody the electrostatic self-co-ordinated field V (ri):

In this approach the decision of a problem for set of electrons is reduced to odnoyoelektronnoj for the account of the assumption of movement of each particle in the average self-co-ordinated field created by all electrons of system. However preyonebrezhenie correlation of electrons considerably reduces efficiency of a method.

In a method of configuration interactions (KV) multielectronic wave function of connection is displayed on determinants Slejtera, opiyosyvajushchim system in all possible electronic conditions (1.1.6.).

Each determinant is under construction of the backs-orbitalej answering basic or one from raised one-electronic conditions. Using this approach it is possible to receive the exact decision of equation SHredingera within the basic set used for approximating orbitalej [71, 74, 75, 77]. In case of the big basis the number of the raised configurations is very great, therefore isyopolzovanie the yielded settlement method is limited by quantity of the configurations answering to excitation only of some number of electrons. Advantage meyotoda that it is applicable to the description of excited states, systems with from -

Covered covers and nonequilibrium systems (for example, dissociating moyolekul).

In a basis of a settlement method of valence bonds representation that communication between two atoms in connection is formed for the account of nationalisation of one or several pairs electrons has laid down. Two basic concepts of the theory valentyonyh communications (hybridization nuclear orbitalej and a resonance of initial structures) have been developed pollingom [76]. Basic position of a method is the thesis about preservation of individuality of atoms in a molecule, and bonding between atoms is considered as result of the influence result ining obobshchestvyoleniju of electrons according to requirements of a principle of Pauli [71, 74, 75, 77].

The theory of perturbation represents a method of the approached problem solving of quantum mechanics in which at the first stage equation HarYotri-Foka dares, on the second modification of the received decision for the account vneyosenija corrections is passed. The yielded theory is applicable to a wide range of problems, including to the description of electronic correlations, however convergence of the decision depends from rasyosmatrivaemoj system and used basis [71, 74, 75, 77].

1.2.

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A source: Rusakova Natalia Petrovna. QUANTUM-CHEMICAL STUDY OF THE ELECTRONIC STRUCTURE OF SERO-CONTAINING MOLECULES AND RADICALS. DISSERTATION for the degree of Candidate of Chemical Sciences. Tver - 2015. 2015

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