GaxPy(x y=8)及其阴离子团簇的结构与性质的DFT研究

1、物理化学学报(Wuli Huaxue XuebaoOctober Acta Phys.鄄Chim.Sin.,2006,22(10:12531259Ga x P y(x+y=8及其阴离子团簇的结构与性质的DFT研究郭彩红贾建峰郭玲武海顺*(山西师范大学化学与材料科学学院,山西临汾041004摘要用密度泛函理论方法对半导体二元微团簇Ga x P y和Ga x P-y(x+y=8的几何结构、电子态、能量等进行了计算,在B3LYP/6311+G(2df水平下完成结构优化和频率分析.讨论了电荷诱导结构发生变化情况,与中性团簇相比,在阴离子团簇中,GaP键较PP键有利于形成.预测了未知Ga1P-7、Ga2

2、P-6、Ga3P-5、Ga6P-2和Ga7P-1化合物的最稳定结构存在的可能性,得出在Ga x P y和Ga x P-y(x+y=8中,Ga4P4和Ga4P-4比较稳定.给出了两种能差即绝热电子亲合势(E AEA和垂直电离能(E VDE,并与相关文献作比较.Ga4P4和Ga5P3的绝热电子亲合势与实验值相当吻合.布居分析表明,磷化镓团簇的成键属于混合键型.关键词:密度泛函理论,Ga x P y和Ga x P-y团簇,布居分析,垂直电离能,绝热电子亲合势中图分类号:O641Study on the Structure and Property of the Neutral Ga x P y(x+

3、y=8and Anionic Gallium Phosphide Clusters Using DFTGUO,CaiHong JIA,JianFeng GUO,Ling WU,HaiShun*(School of Chemistry and Material Science,Shanxi Normal University,Linfen041004,P.R.China Abstract Structure,electronic state,and energy of semiconductor binary microclusters,Ga x P y and Ga x P-y,having

4、eight atoms have been computed using density functional theory(DFTmethod.Structural optimization and frequency analysis are performed at the B3LYP/6311+G(2dflevel.The chargedinduced structural changes of these anions have been discussed.The strong GaP bond is favored over the PP bond in Ga x P-y(x+y

5、=8,in comparison with the corresponding neutral cluster.The calculations predict the existence of previously unknown isomers(i.e.Ga1P-7,Ga2P-6, Ga3P-5,Ga6P-2,and Ga7P-1.Among different Ga x P y and Ga x P-y(x+y=8clusters,Ga4P4and Ga4P-4are more stable.Two types of energy separations are reported in

6、this study,adiabatic electron affinities(E AEAand vertical detachment energies(E VDE,wherever applicalde,and are compared with those described in other published data in the literature.Adiabatic electron affinities for Ga4P4and Ga5P3are in good agreement with those obtained in the experiments.Mullik

7、en population analyses indicate that the bonding in GaP clusters is of a mixed type.Keywords:Density functional theory,Ga x P y and Ga x P-y clusters,Mulliken population analysis,Verticaldetachment energies,Adiabatic electron affinitiesTheoretical and experimental studies on the electronic and geome

8、tric properties of main group IIIV clusters continue to be an active area of research because of their rich chemistry and physics,and perhaps more importantly because of their potential application in the electronics industry12.An important aspect of the chemistry and physics of small clusters invol

9、ves understanding the change in their geometric and electronic properties with an increase in size.Furthering the efforts of several research groups on IIIV clusters,Neumark and coworkers3experimentally investigated the evolution of electronic structure as aReceived:March14,2006;Revised:June5,2006.*

10、Correspondent,Email:wuhs;Tel:03572051375,Fax:03572051375.山西省青年基金(20051011资助项目Editorial office of Acta PhysicoChimica Sinica1253function of size in gallium phosphide semiconductor clusters.In a subsequent work,the authors reported vibrationally resolved anion photoelectron spectra of the lowlying ele

11、ctronic states of small clusters with up to5atoms comprehensively45.Before the study conducted by Neumark and coworkers,Weltner and his associates6had investigated the IR absorption spectra of GaP, GaP2and Ga2P isolated in a4K argon matrix.Several theoretical investigations of gallium phosphide clus

12、ters have been carried out719.Andreoni7employed the CarParrinello molecular dynamics method to study the structure, stability,and melting point of(GaPn clusters with n=25.Costales et al.8studied the structural and vibrational properties of small stoichiometric(GaPn clusters with n=13within the frame

13、work of density functional theory(DFT.The first small GaP fullerene cage was proposed with ab initio molecular dynamics simulations16.Korambath et al.17studied the(hyperpolarizability of GaP clusters by ab initio timedependent HartreeFock method. Inspired by the pioneering work of Neumark and cowork

14、ers on anion photoelectron spectra of Ga x P y clusters3and based on the previous reports on binary semiconductor clusters915,the structures,electronic states and vibrational frequencies for Ga m P-n (m+n5clusters have been investigated in this study using B3LYP/631G(dmethod18.In the near past,Li et

15、 al.19studied the geometric,electronic state of Ga n P and Ga n P2(n=17clusters at the B3LYP/631G(dlevel.Although several studies have been carried out on gallium phosphide,the investigations on larger clusters have scarcely been reported,and calculations of Ga x P y and Ga x P-y(x+y=8clusters have

16、neither been systemically studied.In the present study, the calculations on Ga x P y and Ga x P-y(x+y=8species were performed using the B3LYP level of DFT to provide more reliable ground state geometries,the highest occupied molecular orbital and the lowest unoccupied molecular orbital(HOMOLUMO ener

17、gy gap,and theoretically calculated IR vibrational frequencies at the corresponding optimum structures.A reliable theoretical prediction would be established for those gallium phosphides in the absence of experimental results and in some cases to challenge existing experiments.The choice of DFT has

18、been fully justified for studies on semiconductor system due to the fact that it is an ab initio tool and includes the electron correlation effect which has been found necessary for gallium phosphide clusters at relatively low computational cost1819and other aspect.1Computation methodThe basis set f

19、ollowed in this study was the6311+G(2df oneparticle basis set2021.Restricted methods were used for all closedshell systems,whereas unrestricted methods were employed for the openshell species.Geometrical optimizations were computed using the B3LYP functional.Frequency analyses are also performed at

20、the same theoretical level to check whether the optimized structures are transition states or true minima on the potential energy surfaces of corresponding clusters.All the most stable Ga x P y and Ga x P-y clusters that were obtained were characterized as true minima without imaginary frequencies.F

21、urthermore,adiabatic electron affinities(E AEA of Ga x P y and vertical detachment energies(E VDEof Ga x P-y were calculated.Some of them are compared with the available experimental values.The adiabatic electron affinity is defined as the energy difference between the neutral cluster and its corres

22、ponding anion, that isE AEA=E(optimized neutral-E(optimized anion,where both the neutral cluster and its radical anion are in the lowest electronic states.The vertical detachment energy is defined as the energy difference between the fully optimized anion cluster and the related neutral cluster with

23、out relaxation,that isE VDE=E(neutral at optimized anionic geometry-E(optimized anion.All calculations were carried out using the Gaussian 03program22.2Results and discussionThe ground state geometric sketch figures of Ga x P y and Ga x P-y(x+y=8clusters are shown in Fig.1,where“n”represents neutral

24、 clusters and a represents anion clusters.The corresponding geometric parameters of Ga x P y and Ga x P-y(x+y=8are listed in TableGa1P7and Ga1P原7The equilibrium geometries of the1Aground state of neutral Ga1P7and the2Aground state of Ga1P-7are displayed in Fig.1 (1n and1a.The neutral Ga1P7str

25、ucture is similar to the ground state of P823,the substitution of one P atom by one Ga atom in the wedgeshaped C2v configuration of P823,and the C s could be considered as the distortion of C2v.There exist two kinds of GaP bonds and five kinds of PP bonds in structure(1n. With the addition of an ext

26、ra electron to Ga1P7to form Ga1P-7, the symmetry does not change,but bond distances and bond angles change.For example,bond distances R Ga2P3and R Ga2P4are1254No.10WU,Hai Shun et al :Study on the Structure and Property of the Neutral Ga x P y (x +y =8and Anionic Gallium Phosphide all longer than tho

27、se of the neutral cluster by about 5.0%and 6.3%,bond angles P3Ga2P7and P3Ga2P4decrease in size by 16.1%and 7.2%,respectively.And P P bond lengths are all shorter than those of the neutral cluster.Although no experimental ortheoretical data are available for either Ga 1P 7or Ga 1P -7,the cal culation

28、s in this study should facilitate the analysis of future data.The theoretical E AEA and E VDE are 2.20eV and 2.66eV,respectively.The difference between E AEA and E VDE is attrib uted to the considerable geometric distortions in geometrybetween Ga 1P 7and Ga 1P -Ga 2P 6and Ga 2P -6The geometri

29、es of the 1A 1ground state of Ga 2P 6and its 2A ground state anion are shown in Fig.1(2n and 2a.As was the case for Ga 2P 6,the optimized structure is a distorted cube structure with a C 2v symmetry that is similar to the low lying state of P 8(O h ,which was derived by the substitution of two P ato

30、ms with two Ga atoms in the structure of P 823.With the addition of an extra electron to Ga 2P 6to form the anion,large distortions occurred ingeometry because of John Teller effect.The Ga 2P -6anion displaysC 1wedge shaped structure,which is similar to structure (1a.The calculated values of E AEA a

31、nd E VDE are 1.56eV and 2.64eV,respectively.The difference between E AEA and E VDE isdue to the strong distortion in geometry between Ga 2P 6and Ga 2P -Ga 3P 5and Ga 3P -5The ground state of Ga 3P 5has C 3v (1A 1structure (3n,which can be derived from the structure of P 8by the substitution o

32、fthree P atoms by three Ga atoms.The anion Ga 3P -5also has C 3vsymmetry (3a,and the addition of an electron to the neutral isomer results in an increase in bond length R P P and a decrease in bond angle P2P1P5.There are two kinds of Ga P bonds and one kind of P P bonds in structures (3nand (3a.The

33、calculations of this study predict that the E AEA and E VDE are 2.00eV and 2.13eV,respectively.No photoelectron measurements have yet been performed for this cluster.The values of E AEA and E VDE are close to each other because of the small geometric changes between the neutral and its corresponding

34、 anion.2.1.4Ga 4P 4and Ga 4P -4The lowest energy structure of Ga 4P 4has C 2(1A symmetry,which can be derived from the amalgamation of Ga Ga edges of two trigonal bipyramidal structures of Ga 3P 218and then the Fig.1The lowest electronic state geometries of Ga x P y and Ga x P -y (x +y =8clustersn d

35、enotes neutral clusters and a denotes anionclusters.1255Acta Phys.鄄Chim.Sin.(Wuli Huaxue Xuebao,2006Vol.22 formation of one additional PP bond.A T d(1A1isomer locatesat1.11eV above the ground state.With the addition of an extraelectron to the neutral Ga4P4to form the anion Ga4P-4,the symmetry change

36、s from C2to T d.The ground state of Ga4P-4has T d(2A1structure(4aand is the most energetically favored among isomers.It can be viewed as a fusion of two tetrahedrons of GaP3and PGa3which are rotated with respect to each other.As wascase for Ga4P-4,bond lengths of0.2421nm was obtained usingthe calcul

37、ations described in this study for the identical GaPbonds.The calculated values ofE AEA andE VDE are predicted tobe2.26eV and3.42eV,respectively.The predictedE AEA forGa4P4is in satisfactory agreement with the PE spectrum given byfor Ga4P-4,which is smaller than the predicted values obtained inthis

38、study.2.1.5Ga5P3and Ga5P-3HOMOLUMO gap of structure(5nis greater than that of anyother lowlying states,and the energy of structure(5nis thelowest of all the lowlying states.These may explain the stabilization of the structure(5n.Strong PP bond is favored overGaP bonds in Ga5P3.With an additional ele

39、ctron to the neutralto form Ga5P-3(5a,the symmetry does not change;however,thebond distances and bond angles changed.The PP bond in theanion is shorter than that in the neutral cluster,which indicatesthat the interaction between the two P atoms is enhanced.The calculated values of theE AEA for Ga5P3

40、and theE VDEfor Ga5P-3are2.22eV and2.60eV,respectively.The theoreticalvalues ofE AEA andE VDE are lower than the correspondingforE VDE3.The energy difference betweenE AEA andE VDEis attributed to structural relaxation.2.1.6Ga6P2and Ga6P-2Li et al.19calculated the geometry and energy gap of Ga6P2 clu

41、ster.They predicted that the ground state of Ga6P2has strong PP bond at B3LYP/631G(dlevel.However,in the calculation obtained in this study,it has been found that the D3d(1A1gstructure(6nwith strong GaP bonds is more stable in energy by 72.7kJmol-1than the C s(1Astructure19at the same level.The HOMO

42、LUMO energy gap of structure(6nis also0.30eV greater than that of Lis structure.Hence the stabilization of structure(6nshould be accounted for.The ground state of Ga6P2has six identical GaGa bonds and six identical GaP bonds. With the addition of an extra electron to the neutral Ga6P2to form Ga6P-2,

43、the symmetry remains unchanged;however,the geometric parameters change slightly.Compared with the neutral cluster, the GaP bond distance is longer by1.4%and the GaGa bond distance is shorter by0.9%in the anion.The theoretical values ofE AEA andE VDE are2.00eV and 2.44eV,respectively.Although no phot

44、oelectron measurements are available for this cluster at present,the calculations described *n denotes neutral clusters and a denotes anion clusters.Table1Distances between two atoms in Ga x P y and Ga x P-y (x+y=8clustersClusters Bondlength(nmClusters BondBond typeP(1-P(3P(2-P(3P(2-P(5P(3-P(5P(5-P(

45、6Ga(8-P(1Ga(8-P(2P(1-P(2P(1-P(3P(2-Ga(4P(2-P(6P(3-P(7P(1-P(2P(1-Ga(6Ga(4-P(5Ga(1-Ga(2Ga(1-P(4Ga(1-Ga(5Ga(1-P(7Ga(2-P(3P(3-P(4P(4-P(8P(1-Ga(3P(1-Ga(4P(1-Ga(5P(1-P(7P(2-Ga(3P(2-Ga(4Ga(1-P(2Ga(1-Ga(3Ga(1-Ga(2Ga(1-Ga(3Ga(1-P(4Ga(2-P(4Ga(3-P(4Bond typeP(1-P(3P(1-P(5P(1-P(6Ga(2-P(3Ga(2-P(4P(3-P(5P(4-P(5Ga

46、(1-P(2Ga(1-P(4Ga(1-P(6P(2-P(3P(2-Ga(5P(3-P(4P(3-P(7P(4-P(7Ga(5-P(6Ga(5-P(8P(6-P(8P(7-P(8P(1-P(2P(2-Ga(3Ga(3-P(4Ga-PP(1-Ga(3P(1-Ga(4P(1-Ga(5P(1-P(7P(2-Ga(3P(2-Ga(4Ga(1-P(2Ga(1-Ga(3Ga(1-Ga(3Ga(1-P(4Ga(2-Ga(3Ga(2-P(4Ga(3-P(41256No.10WU,Hai Shun et al :Study on the Structure and Property of the Neutral

47、Ga x P y (x +y =8and Anionic Gallium Phosphide Table 4Mulliken population analyses for the ground electronic state of Ga x P y clustersStructure Gross population (q Natural electron configuration Charge (e 1nGa (8 2.424s (1.224p (1.184d (0.017p (0.010.578P (1 5.243s (1.723p (3.473d (0.045p (0.01-0.2

48、51P (2,7 5.173s (1.753p (3.363d (0.055p (0.01-0.174P (3,4 4.973s (1.733p (3.183d (0.055p (0.010.019P (5,6Ga (4,8 2.454s (1.894p (0.544d (0.017p (0.010.550P (1,5 5.013s (1.693p (3.263d (0.055p (0.01-0.012P (2,6 5.503s (1.713p (3.723d (0.054p (0.015p (0.01-0.499P (3,7Ga (4,6,7 2.584s (1.254p (1.304d (

49、0.016p (0.017p (0.010.436P (1,3,8 5.263s (1.753p (3.463d (0.045p (0.01-0.267P (2 4.973s (1.573p (3.313d (0.074p (0.015p (0.010.022P (5Ga (1,5 2.894s (1.444p (1.414d (0.026p (0.017p (0.010.121Ga (2,6 2.524s (1.834p (0.674d (0.016p (0.010.482P (3,7 5.423s (1.733p (3.633d (0.055p (0.01-0.427P (4,8Ga (3

50、 2.744s (1.424p (1.294d (0.026p (0.010.269Ga (4,8 2.484s (1.854p (0.614d (0.016p (0.010.518Ga (5 2.354s (1.924p (0.426s (0.010.653Ga (6 2.714s (1.424p (1.294d (0.026p (0.010.268P (1,7 5.713s (1.733p (3.923d (0.054p (0.01-0.721P (2Ga (1,6,7 2.864s (1.714p (1.124d (0.026p (0.010.138Ga (2 3.154s (1.614

51、p (1.474d (0.056p (0.02-0.139Ga (3,5,8 2.544s (1.794p (0.734d (0.016p (0.010.456P (4Table 3Total energies,zero 鄄point vibrational energies,andenergy gaps of Ga x P y and Ga x P -y clustersTable 2Harmonic vibrational frequencies and IR intensitiesofthe ground state ofGa x P y and Ga x P -y (x+y =8clu

52、stersSpecies Vibrational modefrequency,(cm -1,and IR intensity (km mol -1,in parenthesesGa 1P 7A :116.5(1.1A :371.2(6.8A :490.5(1.7Ga 2P 6A 1:50.7(1.2B 1:278.8(60.6A 1:513.2(0.3Ga 3P 5E :141.5(0.0A 1:386.3(6.5E :442.2(5.0Ga 4P 4A :43.4(0.0B :140.0(16.2B :463.8(8.0Ga 5P 3A :10.4(0.0A :280.8(63.8A :36

53、4.8(17.5Ga 6P 2E g :39.3(0.0A 2u :314.6(30.5A 1g :325.4(0.0Ga 7P 1A :32.7(0.0E :319.6(71.7E :319.6(71.7Ga 1P -7A :115.1(0.7A :269.7(7.0A :487.5(1.1Ga 2P -6A :83.6(1.4A :399.7(12.3A :487.3(5.2Ga 3P -5E :5.2(8.9A 1:352.1(15.0E :379.9(8.9Ga 4P -4E :135.9(0.0T 2:349.9(26.3T 2:349.9(26.3Ga 5P -3A :29.2(0

54、.4A :301.8(75.3A :380.6(0.5Ga 6P -2E g :36.0(0.0A 2u :333.4(55.3A 1g :343.8(0.0Ga 7P-1Cluster SymmetryStateTotal energies(a.u.Zero energy (kJ mol -1Energy gaps(eV*Ga 1P 7C s 1A -4314.6197132.795 2.82Ga 2P 6C 2v 1A 1-5898.1389728.696 3.50Ga 3P 5C 3v 1A 1-7481.6295728.976 2.83Ga 4P 4C 21A-9065.1288223

55、.412 2.62Ga 5P 3C s 1A -10648.6168018.837 2.62Ga 6P 2D 3d 113.903 2.08Ga 1P -7C s 2A -4314.7004131.791 2.75 2.21Ga 2P -6C 12A-5898.1962228.394 2.15 1.79Ga 3P -5C 3v 2A 1-7481.7031025.162 1.54 2.78Ga 4P -4T d 2A 1-9065.2119825.232 3.11 1.74Ga 5P -3C s 2A -10648.6984118.045 2.27 2.13Ga 6P -2D 3d 2A u

56、-12232.1985116.640 1.65 1.64Ga 7P -1C 3v2A 2*and denote different orbitals respectively.12571258 Acta Phys. -Chim. Sin. (Wuli Huaxue Xuebao, 2006 Vol.22 in this study are useful for further experiments. 2.1.7 Ga7P1 and Ga7P1 The equilibrium geometries of the 1A1 ground state of neutral Ga7P1 and the

57、 2A2 ground state of Ga7P are given in Fig.1(7n. Li 1 acterization of these novel structures in photoelectron spectroscopy measurements in future. 2.2 Vibrational frequency analysis and stability A vibrational frequency calculation is important to predict molecular stability. To determine the ground state of clusters, the vibrational frequencies were calculated for these clusters at the B3LYP/6-311+G(2df level. All the ground states that were reported are actually equilibrium states without imaginary frequenci