Quantum mechanics configurational interaction

J. Gao, Monte Carlo quantum mechanical-configuration interaction and molecular mechanics simulation of solvent effects on the n - n blue shift of acetone. J. Am. Chem. Soc. 116, 9324-9328 (1994)... 

The PCM model has been implemented for the calculation of the electronic excitation energies of solvated molecules within the quantum-mechanical configuration interaction method. The respective final expression for the excitation energy from the ground state (0) to the I-th state has the following form... 

The configuration interaction calculation with all possible excitations is called a full Cl. The full Cl calculation using an infinitely large basis set will give an exact quantum mechanical result. However, full Cl calculations are very rarely done due to the immense amount of computer power required. 

Two more accurate quantum mechanical calculations of the two body system have appeared using configuration interaction and Hyllareas functions, as well as a perturbation expansion in R, but still a hard wall potential 245,246) jjjg scheme in... 

However, if the molecular configuration is such as to bring the radical centers into close contact (say, to within some critical distance D), interaction will begin and the two doublet states will collapse since the spins of the two electrons are no longer independent of each other. Quantum mechanics tells us that under these conditions the total number of states is dependent upon the sum of the spin quantum numbers for the two electrons ... 

Sometimes the theoretical or computational approach to description of molecular structure, properties, and reactivity cannot be based on deterministic equations that can be solved by analytical or computational methods. The properties of a molecule or assembly of molecules may be known or describable only in a statistical sense. Molecules and assemblies of molecules exist in distributions of configuration, composition, momentum, and energy. Sometimes, this statistical character is best captured and studied by computer experiments molecular dynamics, Brownian dynamics, Stokesian dynamics, and Monte Carlo methods. Interaction potentials based on quantum mechanics, classical particle mechanics, continuum mechanics, or empiricism are specified and the evolution of the system is then followed in time by simulation of motions resulting from these direct... 

The value of 3 and its dispersion can be theoretically calculated from equation 6, provided a complete set of electron states of the system is known. Such quantum mechanical calculations have been developed based on molecular Hartree-Fock theory including configuration interactions( 1 3). A detailed theoretical analysis of 3 and contributing 1T -electron states has been presented for several important molecular structures. 

The stable configuration for the H—P pair is predicted by all of the quantum-mechanical calculations to have a hydrogen located at the silicon antibonding site (Si—AB). A model is shown in Fig. 7b, where a phosphorus lone pair lies along the (111) axis and is energetically in the valence band. Here, the theoretical predictions of the H vibrational frequency have been mixed, with the H—Si interaction and frequency overestimated by Hartree-Fock and Hartree-Fock-like methods and lower by local-density calculations. 

The theoretical description based on the lattice or cell models of the liquid uses the language contributing states of occupancy . Nevertheless, these states ot occupancy are not taken to be real, and the models are, fundamentally, of the continuum type. The contribution to the free energy function of different states of occupancy of the basic lattice section is analogous to the contribution to the energy of a quantum mechanical system of terms in a configuration interaction series. 

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