Ground state, of atoms and molecules

From the theoretical point of view, the electrophilicity concept has been recently discussed in terms of global reactivity indexes defined for the ground states of atoms and molecules by Roy et al.18 19. In the context of the conceptual density functional theory (DFT), a global electrophilicity index defined in terms of the electronic chemical potential and the global hardness was proposed by Maynard et al.20 in their study of reactivity of the HIV-1 nucleocapsid protein p7 zinc finger domains. Recently, Parr, Szentp ly and Liu proposed a formal derivation of the electrophilicity, co, from a second-order energy expression developed in terms of the variation in the number of electrons.21... 

The arguments are supported by a number of results on prototypical ground and excited states of atoms and molecules. Most of these are compared with results from conventional methods of quantum chemistry, where single basis sets, orbital- or Flylleraas-type, are used. 

The SAC-CI method was proposed in 1978 as an accurate electronic-structure theory for the ground, excited, ionized and electron-attached states of atoms and molecules. The method has been successfully applied to various photochemistry involving more than 150 molecules and established to be a useful method for studying chemistry and physics involving various electronic states. In this article, we gave a brief overview of our SAC-CI applications to the molecular spectroscopy. 

That is, we assume that it is possible to use the Hartree-Fock method to calculate (approximations to) the electronic structure of the ground and excited states of atoms and molecules. However, we make no assumption about the possibility of the computation of the electronic structure of unbound states or states degenerate with unbound states ( resonances ). 

Figure 3.14. Microscopic pictures of the desorption of atoms and molecules via mobile and immobile transition states. Ifthe transition state resembles the ground state, we expect a prefactor of desorption of the order of 10 s h Ifthe adsorbates are mobile in the transition state, the prefactor increases by one or two orders of magnitude. For desorbing...

At thermal equilibrium, according to the Boltzmann distribution (see Section 2.3), the population of atoms and molecules in the excited state can never exceed the population in the ground state for a simple two-level system. 

Photoelectron spectroscopy (PES, a non-mass spectral technique) [87] has proven to be very useful in providing information not only about ionization potentials, but also about the electronic and vibrational structure of atoms and molecules. Energy resolutions reported from PES are in the order of 10-15 meV. The resolution of PES still prevents the observation of rotational transitions, [79] and to overcome these limitations, PES has been further improved. In brief, the principle of zero kinetic energy photoelectron spectroscopy (ZEKE-PES or just ZEKE, also a nonmass spectral technique) [89-91] is based on distinguishing excited ions from ground state ions. 

The effect of pressure on the ground-state electronic and structural properties of atoms and molecules have been widely studied through quantum confinement models [53,69,70] whereby an atom (molecule) is enclosed within, e.g., a spherical cage of radius R with infinitely hard walls. In this class of models, the ground-state energy evolution as a function of confinement radius renders the pressure exerted by the electronic density on the wall as —dEldV. For atoms confined within hard walls, as in this case, pressure may also be obtained through the Virial theorem [69] ... 

The ground-state energies of atoms and molecules where the A-particle Hamiltonian is defined by Eq. (48) may be expressed through three different representations of the 2-RDM and the two-particle reduced Hamiltonian ... 

N. H. March, The local potential determining the square root of the ground-state electron-density of atoms and molecules from the schriklinger equation. Phys. Lett. A 113, 476 78 (1986). 

---