| The atomic level nano-system contains electron spin polarization effect could exhibit peculiar performance in term of magnetic properties,reaction activities,etc.,which has aroused widespread concern in basic research and shown important application value in biomedicine,material science,and even nuclear science.In the nanoscale confined system,uranium and other actinides contain 5f valence shell electrons can generate complex confined electronic structure when interact with other 2p electrons with abundant orbital hybridization and spin polarization effect,which has great significance in foundation and application of designing actinides embedded confined system.Moreover,only considering the spin polarization behavior of 2p electrons,it may have an important effect on the degradation process of organic polymer systems with unsaturated bonded.In detail,we study the electronic structure of the coated 5f element embedded metal boron clusters and the mechanism of the polymer degradation related to spin polarization.So as to have a regular understanding of the electronic structure characteristics of nanoscale systems with significant spin polarization effects.Boron is the first contain p valence electron light element in periodic table.The electron orbitals sp2 hybridization makes it can form a strong covalent bond structure.B40 cage,which is known as the Chinese red lantern cluster,is a typical representative.The actinide element U is rich in lively valence electrons and has important applications in nuclear energy technology.Based on the electron interaction between the p electrons in B40 cage and 5f valence shell electrons in uranium atoms,it is desirable to construct an embedded metal boron cluster,namely,U@B40.In this part,we predict that U@B40 can exist stably based on the DFT method.Surprisingly,the electronic structure is analyzed through orbitals and electron density,etc.,indicating that U@B40 satisfies 32-electron principle of 1S21P61D101F14.The s-,p-,d-and f-type valence electrons of U atoms are filled to form a closed-sell(core-shell)singlet state.In addition,the estimating binding energy is about 8.22 e V that prove the stability of this cluster.Moreover,the calculated infrared and Raman spectra exhibit active vibration modes of U-B40 stretching and pure B40 breathing respectively to assistant assist the future experimental studies.We hope the current findings may add a new member for superatomic family and is also the first theoretical predication actinide embedded system based on the boron cluster.The study of p electrons spin-polarization effect in the carbon-based materials,such as the zigzag edge of graphene and carbon nanotubes,atomic adsorption graphene,has attracted wide attentions.While,in the organic molecular polymer structure,when numerous monomer radicals ?-methylstyrene(AMS)homopolymerize into long chain polymers poly-?-methylstyrene(PAMS),the unsaturated C atoms at both ends of the PAMS carbon chain skeleton each have a dangling bond,which introduced the p-orbital electron spin polarization effect of carbon.In this work,combined spin-polarization with dissociation mechanism,taking PAMS dimer as calculation model to study the dissociation reaction behavior through energy barrier and spin population,etc.The results show that the dimer dissociation has two reaction path.For the spin polarization singlet(antiferromagnetic coupling),the dissociation reaction energy barrier is about 0.03 e V,exothermic reaction.For the ferromagnetic coupling triplet,the dissociation energy barrier is about 0.80 e V,endothermic reaction.And in the two dissociation reactions,the spin polarization showed a spin redistribution characteristic.Polymer degradation is an important topic in chemical engineering and materials science.However,it is difficult to directly observe the intermediates or transition states in a very short time,thus,study the polymer degradation mechanism theoretically is necessary.In this part,we study three typical free radical PAMS tetramers via DFT method.The calculated results show that C-unsaturated(head-unsaturated)reaction needed to overcome the energy barrier is less than that of CH2-unsaturated(tail-unsaturated),indicating C-unsaturated reaction occurred easily.These reactions needed to overcome the energy barrier in the range of 0.58 to 0.77 e V,and the broken of the C-C bond at the chain unsaturated end leads to the dissociation of the alpha-methylstyrene(AMS)monomer.Furthermore,electronic structure also pointed out the dissociation of the monomer AMS is more likely to occur at the C-unsaturated end and the frontier molecular orbitals main located at the unsaturated end.Meanwhile,spin population analysis presented unique spin migration process in free radical type PAMS depolymerization reaction.Actually,in the olefin polymer head-to-tail(H-T)linkage accounted for the majority,but a spot of abnormal arranged,such as,head-head(H-H)or tail-tail(T-T)linkages also can produce,which can affected the polymer degradation and leads us further explore the degradation mechanism of abnormal linkage PAMS.We study the degradation mechanism of two typical abnormal linkage PAMS tetramer.The results show that H-H and T-T reactions needed to overcome the energy barriers are about 0.15 and 1.26 e V,declaring the H-H reaction preferentially occurred.The C-C bond broken near the unsaturated end of the chain results in the AMS being separated one by one.The bond characteristics revealed that the H-H bond strength is weaker than that of T-T,indicating H-H bond is more likely to be broken in the reaction,which consistent with the energy barrier results.Besides,the spin population analysis also presents an interesting spin migration process.Undertaking the DFT studies related to free radical type PAMS tetramer depolymerization mechanism,we launched the dynamics simulation research at atomic level for three typical cis-form linkage PAMS fragments by using the introduction of dispersion correction of density functional tight-binding theory(DFTB-D)method.The results show that in 500~600 K,PAMS degradation corresponds to the depolymerization process,and monomer units fall off mainly occurs in the unsaturated end of the chain.Furthermore,the electronic structures of three fragments indicate that the electrons in the highest occupied molecular orbital(HOMO)and the lowest non-occupied molecular orbital(LUMO)are mainly located at the unsaturated end,which is consistent with the potential energy prediction.In addition,dynamics simulation results show that increase in temperature appropriately can facilitate depolymerization reaction speed up.Moreover,form the energy perspective,the relaxation scans of the C-C bond break process also clearly show that depolymerization reaction occurs at unsaturated end is easier.And spin population analysis reveals that this is closely related to the electron spin polarization of PAMS.Previously,we have studied the degradation mechanism of two unsaturated-ends,one unsaturated-end and abnormal linkage PAMS chain.In this section,we investigated the dissociation reaction mechanism of saturated PAMS chain by –OH and –H respectively.The bond order shows that the bond strength in functional group saturated CH2-end(tail-tail,T-T)is better than that in Cend(head-head,H-H),suggesting the bond near the CH2-end is hard to break in the reaction.The energy barrier calculations about PAMS tetramer,trimer and dimer are also show that the energy barrier needed to overcome of CH2-end dissociation reaction is greater than that of the C-end,indicating the C-end dissociation reaction is prone to occur and conforms to the bond prediction results.Furthermore,it is also found that PAMS dissociates to produce H2 O,H2 and AMS monomer needed energy barrier is increase by digress from the different research models.That is to say that PAMS chain dissociation produces H2 O in this study is the most prefer to occur.It is hoped that the above research can provide references and guidances for the study of polymer degradation mechanism in experiment and theory. |
PDF Full Text Request