Theoretical Study On The Structure And Nonlinear Optical Properties Of All-Metal Eletrides With Excess Electrons

In this thesis,three new kinds of all-metal electride molecules are designed and investigated by the quantum chemical method.Their geometrical structures,electronic structures,and nonolinear optical properties are systemically and detailedly discussed.The main contributions of this thesis are as follows:1.All-metal electride molecules CuAg?Ca7M(M = Be,Mg and Ca)are designed and researched in theory for the first time.In these molecules,a pull-push electron relay occurs.Unusual all-metal polyanions of fourfold negatively charged[Cu-Ag-Be/Mg]4-and[Cu-Ag]4-with 4 extra electrons gained from Ca atoms,push the remaining valence electrons of the Ca atoms forming the multi-excess electrons(N,=10/12).Therefore.these molecules can be described as salt-like[(Ca2+)7(CuAgM)4-]+10e-(M = Be and Mg)and[(Ca2+)8(CuAg)4-]+12e-.In these salt-like molecules,there are extraordinary covalent bonding modes including 2c-2e/3c-2e o-bonding in the polyanions and the Ca2+ cations sharing the diffuse multi-excess electrons.For intriguing nonlinear optical(NLO)response,these all-metal electride molecules display large electronic first hyperpolarizabilities(?0),thus a new class of NLO molecules-all-metal electride NLO molecules emerge.Meanwhile,it is also found that manipulating atomic number and position of M is a new strategy to enhance ?0.As a result,the CuAg@Ca7Mg(1)exhibits considerable ?0(1.43 x 104 au)being 16 times the?0 sum of two isolated CuAg and Ca7Mg(1)subunits,which deeply reveals the fundamental origin of considerable ?0,namely the multi-excess electrons generated by subunit interaction.These all-metal electride molecules have the infrared(IR)transparent region of 1.3-6 ?m,and hence are new IR NLO molecules.Besides electronic contribution ?0,the large effects of vibrations on static first hyperpolarizabilities of these all-metal electride molecules are also estimated.Thus,this work opens a new research field of all-metal electride IR NLO molecule.2.For novel all-metal electride,a multicage chain structures[(Ni?Ge9)Ca3]n(n=1-4)with all real frequencies are obtained theoretically for the first time.In the structure of n = 1,the Ni?Geg metal cage as the shortest chain skeleton is surrounded by non-bridge Ca atoms.In the structures of n = 2-4,Ni@Ge9 metal cages are connected by bridge Ca atom pair(s)forming new hybrid multicage chain skeletons surrounded by non-bridge Ca atoms.And interesting pull-push electron relay occurs.The chain skeleton pulls valence electrons from non-bridge Ca atoms forming skeleton polyanion,and then formed polyanion pushes remaining valence electrons of the Ca atoms forming excess electrons.The excess electron numbers are Ne = 2,0,4,4 for n = 1,2,3,4,respectively.It is shown that these structures with excess electrons are molecular all-metal electride multicage chains,unexpectedly,and the structure(n = 2)without excess electron is a Ca salt.For nonlinear optical(NLO)response,the electride chains have large static first hyperpolarizabilities(?e0).And?e0 increases strongly from 9321(n = 1,Ne = 2)to 54232 au(n = Ne = 4),which exhibits that significant cage number and excess electron number effects on NLO response.Besides electronic contribution(?e0)to static first hyperpolarizability,the large vibrational contribution(?e0)are also revealed,and the ratios of ?nr0/?e0 are 0.18-1.17.Moreover,the frequency-dependent values ?e(-2?;?,?)and ?e(-?;?,?)have also been estimated.Especially,the evolutions of prominent cage number effects on,?e0??nr0??e(-2?;?,?)and ?e(-?;?,0)are similar.Then a new design strategy of enhancing NLO response by increasing metal-cage number is obtained.Hence,these molecular all-metal electride multicage chains as novel nanorods are promising new NLO nanomaterials.3.Focusing on the interesting new concept of all-metal electride,centrosymmetric molecules e-+M2+(Ni@Pb12)2-M2++e-(M = Be,Mg and Ca)with two anionic excess electrons located at the opposite ends of the molecule are obtained theoretically.These novel molecular all-metal electrides can act as infrared(IR)nonlinear optical(NLO)switches.Whereas the external electric field(F)hardly changes the molecular structure of the all-metal electrides,seriously deforms their excess electron orbitals and average static first hyperpolarizabilities(?e0(F)).For e-+Ca2+(Ni@Pb12)2-Ca2++e-,a small external electric field F = 8 ×10-4 au(0.04 V/A)drives a long-range excess electron transfer from one end of the molecule through the middle all-metal anion cage(Ni@Pb12)-to the other end.This long-range electron transfer is shown by a prominent change of excess electron orbital from double lobes to single lobe,which forms an excess electron lone pair and electronic structure Ca?((Ni@Pb12)2_Cat++2e-.Therefore,the small external electric field induces a dramatic ?e0(F)contrast from 0(off form)to 2.2x106 au(on form)in all-metal electride molecule Ca(Ni@Pb12)Ca.Obviously,such switching is high sensitive.Interestingly,in the switching process,such long-range excess electron transfer does not alter the valence and chemical bond nature.Then,this switching mechanism is a distinct nonbonding evolution named as electronic structure isomerization,which means that such switching has the advantages of being fast and reversible.Besides,these all-metal electride molecules also have rare IR transparent characteristic(1.5-10?m)in NLO electride molecules,and hence are commendable molecular IR NLO switches.Therefore,this work opens a new research field of electric field manipulated IR NLO switches of molecular all-metal electrides.4.To extend the interesting new concept of all-metal electride,a series of endohedral all-metal electride cages 2e-Mg2+(M@E12)2-Ca2+(E= Ge,Sn,and Pb;M =Ni,Pd,and Pt)have been designed and investigated theoretically using exchange-correlation functional CAM-B3LYP.In these electride cage molecules with excess electrons,interesting pull-push electron transfer relay occurs.The metal cage-@n12 first pulls valence electrons from Ca atom forming polyanion(M@E-12)2,and then the formed polyanion pushes valence electrons of Mg atom out its valence shell generating the isolated excess electrons that characterize this species as all-metal electrides.These endohedral all-metal electride cages display large electronic first hyperpolarizabilities(?e0)and then they could have a potential application as new kind of second-order nonlinear optical(NLO)material.We have explored the structure-property relationships,which are significant.It is shown that,for a given central atom,the all-metal electrides with a Sn-cage corresponds to the largest ?e0,whereas,for a given metal cage,the all-metal electrides with Ni as central atom corresponds to the largest?e0.Owing to the two effects,the endohedral all-metal electride cage 2e-Mg2+(Ni@Sn12)2-Ca2+ exhibits the largest ?e0 value(16893 au).The same conclusions are also valid for the frequency-dependent ?e(-2?;?,?)and ?e(-?;?,0).Moreover,we have also explored the role of the vibrational contribution on the largest components(in x-axis)of static ? for endohedral all-metal electride cages.The vibrational contributions are significant for new all-metal electride NLO properties and therefore should be considered in the design of new NLO all-metal electrides.