Studying the interaction theory in H2SO4...HNO...(H2O)n clusters (n = 0-2)

Master of Chemistry (Chemical-Physics orientation)

Abstract

In the present work, he studied the theory of stable structures, bond energies and interaction in H2SO4...HNO...(H2O)n clusters (n = 0-2) at the MP2/aug-cc-pVDZ computational level. became. The presence of one and two H2O molecules strengthens the interaction between HNO and H2SO4 molecules, and this indicates the positive role of H2O molecules in capturing and trapping HNO molecules by suspended H2SO4 particles. AIM theory was used to show the path of interactions and the electron density of the critical points of cluster bonding, and then multi-body interaction was analyzed. Contraction of bond length and blue shift of N-H bond stretching frequency occurs as a result of hydrogen bond formation. Based on EDA analysis, it has been shown that electrostatic and polarization effects contribute more to the stability energy of clusters.

Introduction

One of the foundations of new physics is quantum mechanics. The term quantum mechanics was first proposed by Born in 1924 [1]. Quantum mechanics is the correct description of the behavior of electrons. From a theoretical point of view, in quantum mechanics, every property of a single atom or molecule can be predicted exactly, but in practice, the equations of quantum mechanics have not been accurately solved for any chemical system except the hydrogen atom [2]. Quantum chemistry is the application of quantum mechanics in chemistry-related problems. For example, in the field of physical chemistry, quantum mechanics is used in the following cases:

Calculation of thermodynamic properties of gases (such as entropy, heat capacity)

Interpretation of molecular spectra, in order to help determine molecular properties (such as length, bond angles and dipole moments)

Inspection and calculation The properties of transition states in chemical reactions, in order to estimate the rate constant [3].

A look at computational chemistry

With the passage of time, the need for computer science in the world increases. In the field of basic sciences, computer science has taken effective steps and the proof of this is the design and production of hundreds of software, which make calculations easier with software. Computational chemistry [1], which is also called molecular modeling [2], tries to obtain results related to chemical problems using computers. The questions that are generally investigated computationally are:

Molecular geometry

Energy of molecules and transition states

Chemistry reactivity

NMR, UV, IR

Interactions of a substance with enzyme and physical properties of substances [1]. 

1- Computational methods:

In computational chemistry, the methods are divided into two categories:

1- Method based on molecular mechanics[3] MMM

2- Method based on electronic structure[4] ESM

In both mentioned methods, the same foot calculations are performed:

1- Energy calculations for a specific molecular structure

2- Optimizing the geometric structure that is placed in the minimum potential energy level.

3- Calculation of vibration frequencies caused by movements The interior of molecules appears [4].

1-1) Method based on molecular mechanics (MMM)

The molecular mechanics method, which is also called the empirical force field (EFF), uses the laws of classical physics to predict the structure and properties of molecules.

There are various methods based on molecular mechanics. Each one is characterized by its own force field.In this method, the molecule is considered as atoms that are placed together through bonds. Molecular mechanics describes energy as a function of geometric degrees of freedom such as bond length and angle in terms of force field. Molecular mechanics performs calculations based on interactions between nuclei. Meanwhile, electron effects in the force field are considered during optimization. This approximation makes molecular mechanics calculations less expensive in terms of computer and allows them to be used for large systems as well. The limit for which parameterization has been done gives favorable results and no force field can be used for all molecular systems.

2- Ignoring electrons in this method has caused this method to have nothing to say about any chemical problem in which electron effects are important [4].

A number of programs in molecular mechanics are used, are: AMBER, CHARMM, CHEAT, CFF, GROMOS, MM1... MM4. MM2 and MM3 molecular mechanics programs designed by Allinger[5] and his colleagues are very common. Meanwhile, AMBER and CHRAMM molecular mechanics programs have been developed for protein and nucleic acid analysis [5]. The fact that electrons and other microscopic particles exhibit wave behavior in addition to particle behavior indicates that electrons do not follow classical mechanics. The mechanism that microscopic systems follow is called quantum mechanics, because one of the key aspects of this mechanism is the quantization of energy.

The laws of quantum mechanics were discovered by Schr?dinger[6] in 1926. In quantum mechanics, the state of a system is determined by a mathematical function ? (Psi) called the wave function [2].

According to a fundamental principle in quantum mechanics, there is a quantum mechanical operator corresponding to each physical quantity (such as energy and momentum). Hamilton[7] presented another form of Newtonian motion equations by introducing the Hamiltonian function for the system. The Hamiltonian operator of quantum mechanics is shown as follows: And the potential is formed. The possible values ??for the energy of a system are specific values ??of the energy operator ?. Applying as a special function ?, the equation is written as follows:

?? () = E)

   The dipole properties of the molecule can be calculated in principle by solving the Schr?dinger equation for the molecule. The Hamiltonian operator ? for a molecule is as follows:

?e = KN + Ke + VNN + VNe + Vee

Ke and KN are kinetic energy operators for electrons and nuclei, respectively. VNN and VNe are the potential energy of repulsion between nuclei and the potential energy of attraction between electrons and nuclei, respectively. Finally, Vee is the potential energy of repulsions between electrons. With this Hamiltonian operator ?, it is extremely difficult to solve the Schr?dinger equation. To solve this equation, we need several approximations, one of them is the Born-Oppenheimer approximation.