Study On Cooperativity Of Small Molecular Clusters By Density Functional Reactivity Theory

Density functional activity theory is developed from the conceptual density functional theory,which aims to directly describe molecular activity from the perspective of electron density.Cooperativity is caused by the interaction between two or more molecules,which makes a single molecule more compact or looser when it polymerizes into clusters.In this paper,ARnB as the general form,we define the interaction energy per building block as a measure:En=(E-nER-EA-EB)/n,where E is the total energy of the whole system,n is the number of building blocks included in the system,R is the building block,A and B are optinal ingredients serving as either the core or terminal motifs.If En decreases as n increases,the system is positively cooperative,otherwise,it is negatively cooperative.There is a result that homogenous electric neutrality system Arn and(H2O)n(n=1-20)are positive cooperativity,charged system(H3O+)(H2O)n(n=1-20)is negative cooperativity.In this work,inspired by the results from previous work,we continue the pursuit by focusing on the cooperativity of small molecular clusters,and systematically research the characteristics and original of small molecular clusters in three parts.(1)The question we are trying to answer in this part is whether or not ionic systems are always negative cooperativity.we set to examine the behavior of argon clusters up to 20 repeating units with one lithium cation,Li+Arn(n=1-20),and one fluorine anion,F-Arn(n=1-20),respectively.We employed two total energy partition schemes from density functional theory and the information-theoretic quantities,and thermochemistry quantities.The results show that as the number of atoms in the cluster increases,the enthalpy change in thermodynamics and Gibbs free energy change have a strong correlation with their interaction energy.For the negative cooperativity of ion clusters,it is found that the exchange correlation energy and electrostatic energy both contribute to the system,and the information gain and 2nd Renyi entropy are strongly linearly correlated.(2)In order to verify whether or not the cooperativity of the homogenous molecular systems is positive and charged molecular systems is negative,in the molecular systems(HF)n,(CO2)n,Cl2Arn,NH3(H2O)n,Li+(H2O)n,F-(H2O)n(n=1-20),employ the same research methods.The results that prove the homogeneous molecular systems are positive cooperativity,but for charged molecular systems they are negative cooperativity.We found that positive cooperativity is dominated by the exchange-correlation interaction and steric effect,but the negative cooperativity is dictated by the electrostatic interaction.(3)We aim at the(H2O)+n and(H2O)-n(n=1-20)systems,the results show that the charged system is negatively cooperative.Using the formulas and theories proposed before,the analysis found that the cooperativity is strongly related to the Gibbs free energy and enthalpy change of the system.Through energy analysis,these results clearly show that there is no single interaction within these two systems,but it is found that electrostatic energy has a strong influence on both systems.Simultaneously,the information gain and the 2nd-order Renyi entropy are strongly correlated with the interaction energy in these systems.In this work,I take different clusters of small molecular systems as objects.To find out what is the main contributions for causing cooperativity for various systems,employing the energy decomposition scheme and information theory from density functional theory.It is found that the causes of cooperativity in different systems are not the same,but the results are unified,that is,homogeneous molecular systems are positively cooperative,whereas charged molecular systems are negatively cooperative.We studied a kind of weak interaction from different perspectives in this paper—cooperativity.It expand the application of DFRT.Our results from this work should have strong implications for better understanding weak interaction such as macromolecular clusters even in biomolecules and protein systems in solutions,and so on.