Investigations On The Mechanic-magneto-optic Dynamics Of Endohedral Metallofullerenes

Endohedral fullerenes are a family of novel functionalized molecular materials,which have promising applications in future micro-and nanoscale devices.Previous investigations show that the configurations of both the outer fullerene cage and the endohedral system will be changed under the influences of stress and strain.And such minor variations could result in the changes of the basic electronic structures and spin density distribution of the endohedral fullerene,which in turn will affect the ground-state and excited-state properties of the entire system.However,the mechanism of strain modulation on the magneto-optic dynamics of finite systems remains undiscovered.In the present proposal,the physical-mechanics theoretical modeling and micro-and nano-mechanics computational methods such as molecular dynamics and first-principles calculations will be extensively adopted to study the structural stability and electronic stability of three different endohedral fullerenes,[Co@C60]+?Co2@C60 and [Ni@B40]-,firstly;And based on the above results,involving the strain effect,to explore the influence and rules of strain modulation on the magneto-optic dynamics properties of the studied molecular systems from the aspect of mechanics.The main work and results of this thesis are as follows:(1)By using Hartree-Fock method,the structural optimizations and frequency calculations are performed on three different endohedral metallofullerenes,[Co@C60]+?Co2@C60 and [Ni@B40]-,respectively,to obtain the stable structure of each endohedral fullerene.The calculations reveal that there are 3 different configurations of [Ni@B40]-.After that,the symmetry adapted cluster-configuration interaction(SAC-CI)method are performed on each endohedral metallofullerenes to get the precise electronic structure and the properties of excited states.(2)Based on the geometry configurations and electronic structures,the analysis of spin density distribution of each endohedral fullerene are performed.The results reveal that the spin densities are mostly localized on embedded magnetic structures for ground state.While for [Co@B40]-,the spin localization of Co atom is decreased significantly on high energy states.(3)Based on ?-process theory,using [Co@C60]+?H-H type Co2@C60 and Hep type [Co@B40]-as examples to investigate the properties of laser-induced spin dynamic process on the three endohedral fullerenes.It reveals that the spin switching process can be achieved on all the three endohedral structures within subpicosecond scale by using the proper parameters of laser pulse.It should be noticed that there are two different spin switching process corresponding to two sets of parameters of laser pulse can achieved on Hep type [Co@B40]-,and the time scales are 400 fs and 1400 fs,respectively.(4)By adding uniaxial strain on H-H type Co2@C60 and Hep type [Co@B40]-,we investigate the strain modulations on structural symmetry,structural stability and spin density distribution of three endohedral fullerenes.The results show that,compared with the relaxed structures,the geometry structures of the stretched fullerenes almost have not changed and still keep the original symmetries.In addition,strain would induce a redistribution of spin density on the Hep type [Co@B40]-,but almost no effect on H-H type Co2@C60.(5)Based on the uniaxial-strain structures and spin density distributions of H-H type Co2@C60 and Hep type [Co@B40]-,we investigate the effect of uniaxial strain on spin dynamic behaviors of the two endohedral fullerenes.It reveals that,for H-H type Co2@C60,larger strain leads to faster spin switching process,and causes less Rabi oscillations in electronic occupation and spin angular momentum during the spin switching scenarios;While for Hep type [Co@B40]-,uniaxial strain can also influence the speed and efficiency of spin switching processes.The fastest switching scenarios can be achieved by adding 0.5% compressive strain,while the time of spin switching process can be significantly expanded under other strain states.In addition,the Rabi oscillation during the spin switching processes can be reduced 0.5% compressive strain and 1.0% tensile strain.(6)We investigate the structural and mechanical properties of boron fullerene B40 by using density function theory(DFT).According to the relationship between total energy of deformed structures and strain,we built the mechanical model for B40 structure with uniaxial tensile and compressive strain.Through investigation of this thesis,it is expected to reveal the mechanism and device principle of the strain-modulated magneto-optic dynamics properties of endohedral fullerenes,and to establish the theoretical basis and provide novel ideas for the design of functional devices based on the endohedral fullerenes.