The Construction Of Potential Energy Surface And Theoretical Study Of Dynamics For The Reaction System Of Metals Hydride

One of the important tools in the study of chemistry is molecular reaction dynamics,which is used to study and to understand the mechanism of chemical reaction by observing chemical reaction at atom and molecular level.The potential energy surface is the premise for the study of reaction dynamics,the reliability of the results of the molecular reaction dynamics is ensured by the veracity of the potential energy surface.The ground state potential energy surfaces(PESs)of the AuH2、NaH2+and Li2H metals hydride system are constructed using the neural network method and ab initio theory in this work.The reaction dynamics are studied using the time dependent wave packet(TDWP)method based on the new potential energy surfaces and the reaction mechanism is discussed.The main work in this paper consists of three parts:(1)The new potential energy surface of AuH2 system is constructed using the neural network method based on 22853 ab initio energy points.The ab initio energy points are calculated by multireference configuration interaction(MRCI)calculations with a Davidson correction using basis sets of aug-cc-pVQZH and cc-pwCVQZ-PPAu.The neural network method is employed to map the AuH2 PES,the root mean square error is only 1.87 meV.The equilibrium position,dissociation energy and harmonic frequency of AuH(1∑+)and H2(X1∑g+)molecule obtained in the new PES agree well with the experimental data.On the new PES,the reaction dynamics calculation of Au(2S)+ H2(X1∑g+)→AuH(X1∑+)+ H(2S)are carried out using TDWP method.Due to the reaction is an endothermic reaction,the reaction exists a threshold about 1.46 eV.The total reaction probabilities of J = 0 shows several resonance peaks appear in the range of the low collision energies.The resonance structures arise from the existence of the well in the minimum energy reaction path of the title reaction.The resonances become broader and less pronounced as the collision energy increase,indicating the shortening of the life time of the collision complexes.The integral cross sections(ICSs)increase with the increasing of collision energy.In the low collision energy range,the resonance structures of ICSs disappear due to the sum over the reaction probabilities of all total angular momentum J.The total differential cross sections(DCSs)shows that both the forward scattering and backward scattering are existing but the forward scattering is obvious and becomes more and more apparent with the increasing of collision energy.(2)A global potential energy surface of the ground state Li2H system is mapped based on the 30000 Ab initio energies.The energies are calculated by MRCI-F12 method and aug-cc-pVTZ basis set.The PES is constructed using the neural network method with the root mean square error of only1.296 meV.Based on the new PES,the dynamical reaction of H + Li2(X1∑g+)→ Li + LiH(X1∑+)is calculated using the TDWP method,and get the information of the reaction probabilities,ICSs,DCSs and so on.There is no threshold,for the reaction is exothermic with absence of the energy barrier on the global minimum reaction path.The ICS is large at low collision,then decreases slowly with the increase of collision energy.From the results of DCSs,at all collision energies,both forward and backward scattering signals exist which can be expected due to the deep well on the PES.The results of DCSs show that the indirect reaction is dominant in H + Li2(X1∑g+)→Li + LiH(X1∑+)reaction.(3)A global potential energy surface of the ground state NaH2+ system is reported using the neural network method.The ab initio energies are obtained from MRCI with a Davidson correction using basis sets of aug-cc-pVXZ(X = Q,5),then extrapolated these energies to the complete basis set limit.Due to the similarity between the Na and Li,they may have lots of similar properties.Through the comparison of the global minimum energy paths of the new NaH2+ PES and the LiH2+ PES finding that the two PESs are similar,only the exothermic energy and the well exist little difference.Based on the new PES,the reaction dynamics calculation of H(2S)+ NaH+(X2∑+)are carried out using the TDWP method.The H + NaH+ scattering reaction on the ground state PES may lead to the following products:H + NaH+ → H2 + Na+(depletion),Ha + NaHb+→Hb + NaHa+(exchange),Ha + NaHb+ → + NaHb+(no reaction),H + NaH+→H + H + Na+(collision induced dissociation).In this paper,the dynamic calculation only contains the first two reaction channels.Firstly,the dynamical results of H(2S)+ NaH+(X2∑+)→Na+(1S)+ H2(X1∑g+)depletion reaction channel are compared with the results of H(2S)+LiH+(X2∑+)→ Li+(2S)+ H2(X1∑g+)reaction.From the comparison of the DCSs for the two reaction systems,it can be found that both forward and backward scattering signals can be observed for H(2S)+ LiH+(X2∑+)→ Li+(1S)+ H2(X1∑g+)reaction at low collision energy,which means that the reaction may have two reaction mechanisms.But for H(2S)+ NaH+(X2∑+)→Na+(1S)+ H2(X1∑g+)reaction,there is only forward scattering signals remain,with the backward signals almost disappearing for all collision energies,which means the direct abstract mechanism dominates in the reaction.Then the exchange reaction Ha + NaHb+-→Hb + NaHa+is calculated,and the dynamical results of the two reaction channels are analyzed.The reaction of H(2S)+ LiH+(X2∑+)is different from the reaction of H(2S)+ NaH+(X2∑+).due to the reaction probabilities of the H(2S)+ LiH+(X2∑+)exchange channel is very small.For the H + NaH+reaction,the exchange channel reaction probabilities increase with increase of collision energy,while the reaction probabilities of the depletion channel decrease with the increase of collision energy.For all collision energies,the reaction probabilities of the depletion channel are larger than the exchange channel.From the DCS results,it can be found that backward signals play main role in the exchange channel Ha + NaHb+ →Hb + NaHa+.