Quantum chemistry is defined as a branch of theoretical chemistry that uses applications of quantum mechanics and quantum field theory. It lies in the borderline of physics and chemistry. That why scientist of both fields made significant contributions. One of those scientists is Erwin Rudolf Josef Alexander Schrödinger. Schrödinger is famous for a equation (Eq. 1-2) he derived that describes how the quantum state of a physical system changes in time. It is the equivalent to Newton’s laws on classical mechanics. There’s also a derivation of a time independent Schrödinger equation (Eq. 3).
EΨ = ĤΨ
Equation 1 Schrödinger equation
ih (δΨ/δt) = ĤΨ
Equation 2 Time dependant Schrödinger equation
ĤΨ = EΨ
Equation 3 Time independent Schrödinger equation
That equation has an eigenvalue of Ĥ. That’s the Hammiltonian operator. It describes the contributions of the system energy. It includes electrons kinetics energy, repulsions between nucleuses and electrons and attractions between nucleus and electrons. When choosing the operator (Hammiltonian) we are choosing a method to solve Schrödinger’s equation. One of those methods is the Density Functional Theory using computational chemistry. Density Functional Theory (DFT)(described in Eq. 4) is used to investigate the ground state electronic structure of a molecule. That method uses the electronic density from the years 1920s by an later that was well developed by Kohn and Hohenber in the 1960s. One DFT method of calculation is the Harthree-Fock theory. Many studies about DFT come from that theory. One of those people that studies DFT and established their own theory are Pierre Hohenberg and Walter Kohn.
Equation 4 Density Functional Theory
Equation 4 also was well studied by Kohn and Hohember. They said that a system or a molecule behavior can be calculated by its electronic density. They demonstrated that a one-one relationship between electron density and wave function. It contains the minimal information of the studied molecule. It is among the most popular and versatile methods available in computational chemistry. This is possible because is one of the easiest way to solve quantum chemistry problems. Computational chemistry is the branch of chemistry that used computer programs to solve chemical problems. It uses results of theoretical chemistry incorporated in a software to calculate geometry, stability, frequencies and predict the physical and/or chemical behaviour of a particle or a molecule. That method is a pre-
cise one known as ab initio calculations due to be the most basic analysis maded on a system or a molecule.
That software is placed in nanobio clusters in the University of Puerto Rico at Rio Piedras. That cluster have recently updated the OS Rocks 5.2 and its storage capacity to 4TB.The new PGI path is /share/apps/pgi. 04/20/2010/ Right now Nanobio has Lustre running, this is parallel file system with a 14 TB of storage allocation and the capacity of writing and reading up to 230 MB/s of aggregate I/O.
Those specifications are enough to work with many moleculecules at the same time. With the DFT, the properties of a molecule can be determined by the use of functionals. One of those functionals is the Unrestricted OPBE.
OPBE is a DFT functional used in Gaussian 03. Is one of the best functional available to calculate the prediction of molecules, especially magnetic sheldings and chemical shifts. Is one of the most recommended method to the study of catalyst molecules.
LANL2DZ is the basis set for the calculations for density functional theory for first row transition metals. That is the acronym of “Los Alamos National Laboratory 2-double-z”. It analyzes the excitation and ionization energies of a molecule. It is well known that LANL2DZ has the ordering of transition metals atomic states shows clearly weaknesses of the density function methods to match the experimental. It is demonstrated that compared with other basis sets, LANL2DZ is more accurate describing real and reproducible data.
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by Eduardo Moró Pérez