Physical chemistry ground electronic state

The fragmentation of a molecule in its ground electronic state is commonly known as unimolecular dissociation [26-28]. [For a recent review see Ref. 29 and the Faraday Discussion of the Chemical Society, vol. 102 (1995).] Because of its importance in several areas of physical chemistry, such as combustion or atmospheric kinetics, there is a high demand of accurate unimolecular dissociation rates. On the other hand, however, the calculation of reliable dissociation rates by dynamical methods (i.e., the solution of the classical or quantum mechanical equations of motion) is, for obvious technical problems, prohibited for all but a few simple molecules. For... 

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. 

Weitz E and Flynn G W1981 Vibrational energy flow in the ground electronic states of polyatomic molecules Advances in Chemical Physics Vol. XLVIl, Photoselective Chemistry part 2, ed J Jortner, R D Levine and S A Rice, pp 185-235... 

By convention in physical chemistry, vibrational levels and rotational levels of the ground electronic state are denoted with double primes, as in i/ and /", respectively. Vibratioiral levels and rotational levels of the excited electronic state are denoted with single primes, as in i/ and /. Often, however, organic photochemists omit the double prime notation for the ground electronic state. Also, the vibrational quantum levels may be denoted as v or V instead of v. 

Today we know that the HF method gives a very precise description of the electronic structure for most closed-shell molecules in their ground electronic state. The molecular structure and physical properties can be computed with only small errors. The electron density is well described. The HF wave function is also used as a reference in treatments of electron correlation, such as perturbation theory (MP2), configuration interaction (Cl), coupled-cluster (CC) theory, etc. Many semi-empirical procedures, such as CNDO, INDO, the Pariser-Parr-Pople method for rr-eleetron systems, ete. are based on the HF method. Density functional theory (DFT) can be considered as HF theory that includes a semiempirical estimate of the correlation error. The HF theory is the basie building block in modern quantum chemistry, and the basic entity in HF theory is the moleeular orbital. 

Here h is the Planck s constant, me the mass of an electron, L the width of the potential well, and n the quantum level, that is, the number of the rung on which the electron is perched like a bird. Let us calculate the energy of the first electron we will place it at the lowest rung, n = 1. A choice of lowest quantum numbers, and therefore the lowest energy, is a natural one it is known as the ground electronic state of a molecule (or an atom, ion, radical,..., a particle). We will label it as Eq. This is an important concept in chemistry and physics. 

Hare PM, Crespo-Hernandez CE, Kohler B (2006) Solvent-dependent photophysics of 1-Cyclohexyluracil ultrafast branching in the initial bright state leads nonradiatively to the electronic ground state and a long-lived lnp state. Journal of Physical Chemistry B 110 18641-18650. 

Due to its excellent balance between accuracy and computational cost, Kohn-Sham density functional theory (KS-DFT) [13,14] is usually the method of choice to investigate electronic ground states and their properties in chemistry and solid-state physics [15,16]. Hartree-Fock (HF) wavefunctions, on the other hand, are the starting point for ab initio electron correlation methods [4,15] which are discussed in Section 4. 

The fact that an electronic state must be antisymmetric under interchange of any two electrons is an expression of the Pauli Principle. It implies also that no two electrons are allowed to be in exactly the same 1-electron state for if we replace V b by a second ipA the antisymmetric combination disappears In a many-electron atom, say, the state of lowest energy (the ground state ) must have electrons spread over different 1-electron states Vu, b> , not more than one in each, even if the energy of the A state is lower than all the others. Were it not for the antisymmetry restriction, the ground state would be the one in which all electrons crowded into i a- atoms would show no shell structure and would collapse into dense and compact clouds of electrons, in the immediate vicinity of their nuclei. It can be argued that the Pauli Principle is perhaps the most important single principle in the whole of physics were it not valid there would be no atoms, no chemistry, no life, no universe as we know it. 

An atom in its ground state adopts a configuration with the greatest number of unpaired electrons. P.W. Atkins, Physical Chemistry, 5th ed., pp. 447 448, W.H. Freeman and Co., New York (1994). Spin correlation refers to the phenomenon in which electrons with parallel spins behave as if they have a tendency to stay well apart and hence repel each other less. 

The DFT of nano-silicate photocatalyst. Density functional theory (DFT) is a computational quantum mechanical modelling method used in physics, chemistry and materials science to investigate the electronic structure (principally the ground state) of many-body systems, in particular atoms, molecules, and the condensed phases. With this theory, the properties of a many-electron system can be determined by using functionals, i.e. functions of another function, which in this case is the spatially dependent electron density. DFT is among the most popular and versatile methods available in condensed-matter physics, computational physics, and computational chemistry. Therefore, the DFT calculation was employed to analyse the effects of modified silicates using different modified methods. 

A hundred years ago results from physics and physical chemistry had already influenced the conceptual status of inorganic chemistry. In the present context, it may be noted, in particular, how the experimental study of electrolysis processes had led to the concepts of cations, anions, and electrochemical equivalents. An important conclusion from these studies was, for example, that the monovalency of silver and the divalency of copper in their normal salts were more than just stoichiometric attributes. This conclusion, based upon integers, gives rise to the most important class of statements in chemistry, which we would like to call qualitative in a strong sense. We shall see further examples of this kind of statement below in connection with oxidation states, atomic electron configurations, and ground state specitications. 

As illustrated in Sect. 2.5, already in 1926 it was remarked [1] that photochemistry is concerned with all of the electronically states of chemical entities, and thus in a sense it is photochemistry that includes chemistry and not vice versa, since ground states are but a particular case of electronic states. Furthermore, comparing the reactivity of excited states with that of the corresponding ground states makes particularly apparent the direct relation between chemical properties and electronic structure of each species and thus the role of the electronic structure in the reactions of chemical species. In view of this situation, it may be thought that all chemistry, through photochemistry, is included in atomic physics, the science that studies the intimate structure of the matter and thus the electronic stmcture of atoms and molecules. This peculiar relation endows photochemistry both with a particularly... 

---