# Numerical Simulation of Interaction between Plasma and Azithromycin Based on Molecular Dynamics
## 1 Introduction  
Nonthermal plasma treatment technology is an emerging technology with promising prospects in various applications. Intensive studies have been made in recent decades to develop this technology, especially in the field of biochemistry, such as [1] for pharmaceuticals [2; 3], surface disinfection [4], tooth bleaching [5; 6; 7; 8], the organic matter treatment of sewage, and [9] water purification.  
Chemical degradation [10; 11; 12; 13] and microbial degradation [14; 15] are commonly used to treat the organic matter in sewage and waste liquids, but both approaches have limitations. The chemical degradation method mainly uses a combination of various chemical reagents to degrade substances, but it may cause secondary pollution due to excess chemical products. As for microbial degradation, microorganisms will develop resistance when degrading antibiotics, making the degradation effect worse. However, nonthermal plasma degradation technology will not have the above problems. The nonthermal plasma can continuously generate an appropriate amount of oxygen-containing active particles which can efficiently react with the pollutants to degrade them, producing eco-friendly products. In the literature [16; 17; 18; 19], the plasma-active-oxygen group was used to improve the degradation rate of many antibiotics. The active-oxygen group and the catalyst could accelerate the degradation of antibiotics without producing pollutants. The literature [20; 21; 22] showed that oxygen-containing free radicals generated by plasma play a vital role in decomposing ofloxacin and other antibiotics, and that the degraded products are mainly carbon dioxide and water, which will not pollute the environment. In the above experiments, only the effectiveness of the oxygen-containing groups on degradation was studied, and the oxidation ability of each active species was not singly identified.  
Despite the large numbers of practical experiments that have been conducted and reported, very few studies have focused on the fundamental mechanisms of plasma degradation of antibiotics, especially at the atomic level. Computer simulations are gradually recognized as a bridge connecting theory and experiment, and molecular dynamics simulations are one of them. Molecular dynamics [23] and reactive forcefields [24] can simulate the breaking and formation of chemical bonds so that the mechanism of interaction between substances can be explained. [PERSON] et al. [25; 26; 27] studied the interaction mechanism of plasma-active-oxygen groups with fatty acids, glucose, cell walls, and other organics through a molecular dynamics and reactive forcefield simulation, which provided strong support for the experimental research. Based on reactive forcefields, [PERSON] et al. [28; 29] studied the mechanisms of surface modification of materials by plasma.  
In this paper, a molecular dynamics and reactive forcefield simulations were used to study the mechanism of the nonthermal plasma degradation of azithromycin. The reactions between the azithromycin molecule with the plasma particles, including hydroxyl, ozone, and an oxygen atom, were also simulated. The specific modeling method will be elaborated in the second section; Section 3 describes the reaction products and pathways; the fourth section focuses on the analysis of the effect of different types and different amounts of active particles on azithromycin molecules; the conclusions and follow-up work will be elaborated in Section 5.