# Computational Chemistry

The Computational Chemistry uses existing programs and methods to be applied to solving specific chemical problems.

Summary

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• 1 Definition
• 2 Aspects it includes
• 3 The Mathematical Methods
• 4 Using approximate methods
• 5 Applications
• 6 Sources

Definition

Computational chemistry is a discipline of Chemistry whose objective is the creation and use of computer programs that serve the purpose of studying the properties of molecules and, to a lesser degree, of extended solids .

Aspects it includes

• Molecular modeling
• Computational methods
• Computer aided molecular design.
• Chemical databases.
• The organic synthesis design.
• The search for data in chemical bases.

Mathematical Methods

Computational Chemistry covers a wide range of mathematical methods that can be divided into two broad categories:

• Molecular mechanics: applying the laws of classical physics to the molecular nucleus without

explicitly consider electrons .

• The quantum mechanics: based on the Schrödinger equation to describe a

molecule with a direct treatment of the electronic structure and which in turn is subdivided into two classes, according to the treatment carried out, semi-empirical methods and ab initio methods (“from the beginning”).

Use of approximate methods

In principle, it is possible to use a method considered “exact” and apply it to all molecules. However, although these are sufficiently well-known and available methods in many software application packages, the computational cost increases factorially (that is, even faster than exponentially) as a function of the number of electrons in the molecule. For this reason, there are approximate methods that seek the balance between precision and computational cost. Computational Chemistry can calculate with great precision and moderate costs the properties of those molecules that have up to 10 electrons. The study of molecules with a few dozen electrons can only be approached using approximation-based methods, as is the case with “density functional theory”. Even larger systems, such as heavy metal- containing molecules , three-dimensional systems, or enzymes, they can only be managed in a diverse way, concentrating interest in a certain area of ​​space or in some electrons in particular, and allowing the rest of them to reproduce by means of pseudo-potentials, by point electric charges, or by classical force fields: they are the so-called hybrid QM / MM methods (anglicism which means “Quantum Mechanics / Molecular Mechanics” or, in Spanish, “Quantum Mechanics / Molecular Mechanics”).

Applications

Computational chemistry can be applied to:

• The computational representation of structures such as atomsand molecules,
• The storage, structuring and search of information on chemical entities,
• Identifying patterns, trends and relationships between different chemical structures and their properties
• The study of structures based on the simulation of force fields
• Models to promote efficient compound synthesis
• The design of molecules that interact with each other, especially for the design of drugs