Ground-state calculations energy results

In order to consider the inversion of Qx(0,0) and Qy(0,0) electronic transition intensities in NH-tautomers of non-symmetrical free-base porphyrins we calculated the ground-state orbital energies of the investigated molecules by a CNDO/2 method using the symmetrized crystal geometry of porphyrin molecule (37,38). On the basis of the above experimental results we must introduce a motionless system of molecular X and Y axes, identically fixed in both tautomers. Then using theoretical MO calculations and the analysis... 

The VB simplified model of ground-state potential energy surface H3 system considered as transition state and stabilization valleys of the H + H2 reaction is also an early problem, belonging to the history of physical chemistry under the name London-Eyring-Polanyi-Sato (LEPS) model that continues to serve as basis of further related developments [17,18], The actual analysis is a new a focus on the JT point of this potential energy surface able to absorb results of further renewed CASCCF type calculations on this important system. 

Table 7 Results o/ab initio calculations on CH2, energy of sBi ground state, geometry, energy separation...

Since DFT calculations are in principle only applicable for the electronic ground state, they cannot be used in order to describe electronic excitations. Still it is possible to treat electronic exciations from first principles by either using quantum chemistry methods [114] or time-dependent density-functional theory (TDDFT) [115,116], First attempts have been done in order to calculate the chemicurrent created by an atom incident on a metal surface based on time-dependent density functional theory [117, 118]. In this approach, three independent steps are preformed. First, a conventional Kohn-Sham DFT calculation is performed in order to evaluate the ground state potential energy surface. Then, the resulting Kohn-Sham states are used in the framework of time-dependent DFT in order to obtain a position dependent friction coefficient. Finally, this friction coefficient is used in a forced oscillator model in which the probability density of electron-hole pair excitations caused by the classical motion of the incident atom is estimated. 

We illustrate the MOVB method by the SN2 reaction between Cl- and CH3C1, and apply this technique to model substitution reactions. We show that the MOVB method can yield reasonable results for the ground state potential energy surface of the Sn2 reaction both in the gas phase and in solution in comparison with MO and ab initio VB calculations. In all calculations, the standard Gaussian 6-31G(d) basis function is used to construct the MOVB wave function. 

It should be remembered that DFT is designed to reproduce the ground-state density of the system under consideration. It is not concerned with excited states and so the relative energy of filled and empty orbitals is not as well defined as in the H F approach. We will see thaf in solid-state calculations, this results in a poor estimation of the band gap for insulators when using LSDA or GGA functionals. To tackle excitations directly, the more computationally demanding time-dependent DFT methodology has been developed and this does allow spectroscopic excitation energies to be calculated [24]. 

All of the ground-state total-energy differences, regardless of basis set or correlation treatments, give essentially the same result. For example, MBPT(2) calculations with the 6-3IG basis favor the gauche conformation over the anti conformation by just 0.04 kcal/mol. The barrier between these two conformers is 0.6 kcal/mol, but the barrier between the two gauche forms is 1.2 kcal/mol. Steric factors will dominate considerations of the relative energies of substituted rotamers. 

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