共查询到20条相似文献,搜索用时 125 毫秒
1.
2.
3.
4.
5.
采用基于第一性原理密度泛函理论的平面波赝势方法,对0.5NdAlO3-0.5CaTiO3晶体进行结构优化,并对其能带结构,态密度和光学性质进行了理论计算.结构优化后晶格参数与实验数据相符合,误差小于1%;能带计算结果表明0.5NdAlO3-0.5CaTiO3为间接带隙,带隙值为0.52eV;费米面附近的能带由Nd-4f,O-2p,Nd-4p,Al-3p,Ti-4d层的电子态密度确定.同时也计算了该结构的介电函数,反射率和复折射率等光学性质. 相似文献
6.
采用密度泛函理论中广义梯度近似对非典型富勒烯C22和过渡金属内掺衍生物M@C22(M=Sc,Ti,V,Cr,Mn,Fe,Co和Ni)的几何结构和电子结构进行计算研究.发现非典型富勒烯C22的基态结构是含有一个四碳环的单重态笼状结构.过渡金属原子的掺入明显提高了体系的稳定性. C-M键既有一定共价性又有一定离子性.磁性、能级图、轨道分布和态密度图分析表明: M原子的3d轨道和碳笼的C原子的原子轨道之间存在较强的轨道杂化. Ti, Cr, Fe和Ni内掺的结构出现磁性完全猝灭现象. Sc和碳笼间是弱反铁磁作用, V,Mn和Co与碳笼间是弱铁磁作用. 相似文献
7.
8.
用从头算方法的MP2和CCSD(T)方法结合cc-pVTZ基组计算了二氯化锗同位素(70GeCl2、72GeCl2和76GeCl2)分子的平衡结构、光谱常数和非谐振力场.二氯化锗的几何结构、转动常数、振转相互作用常数、谐频、非谐振常数、四次和六次离心畸变常数、三次和四次力常数的计算结果与实验结果符合较好,二氯化锗分子的同位素效应较小,可能的原因是Ge同位素的质量变化相对较小.两种方法计算的结果均与实验结果符合,但CCSD(T)方法比MP2计算结果的偏差稍大一些,可能的原因是CCSD(T)方法在描述过共价Cl原子的电子相关时不够充分. 相似文献
9.
采用密度泛函方法,研究了MnxSny(x=2,3,4; y=18,24,30)团簇的几何结构. 发现MnxSn6x+6(x=2,3,4)倾向于形成 Mn 原子内掺入D3d Sn团簇单笼结构,即Mn2Sn18, Mn3Sn24 和Mn4Sn30.而MnxSn6x+12(x=2,3)则倾向于形成由两个小笼连接 而成的双笼结构,即MnSn12-MnSn12 和MnSn12-Mn2Sn18.因此,可望通过控制掺杂Mn 原子的数量来组装成不同结构的MnxSny一维纳米线. 相似文献
10.
采用脉冲激光气相沉积(PLD)方法,在Si(100)晶面上制备了Co:BaTiO3纳米复合薄膜.采用X射线衍射(XRD)结合透射电镜(TEM)方法研究了两种厚度Co:BaTiO3纳米复合薄膜的晶体结构,当薄膜厚度约为30 nm时,薄膜为单一择优取向;当薄膜厚度约为100nm时,薄膜呈多晶结构.原子力显微镜(AFM)分析表明,当膜厚为30nm时,薄膜呈现明显的方形晶粒.采用紫外光电子能谱(UPS)研究了Co的价态和Co:BaTiO3纳米复合薄 相似文献
11.
The parameters of the nuclear magnetic resonance (NMR) spectrum – shielding constants and indirect spin–spin coupling constants – of three isomers of C20 are studied using density-functional theory. The performance of different exchange–correlation functionals is analysed by optimising the geometry for the ring, bowl and cage isomers, followed by a computation of the NMR constants at the optimised structure. The results are analysed and rationalised by performing comparisons of the three isomers with one another and with related systems such as polyynes (for the ring), o-benzyne (for the bowl) and C60 (for the cage). The shielding and spin–spin parameters calculated using the Perdew–Burke–Ernzerhof (PBE) exchange–correlation functional are sufficiently reliable to assist in future experimental NMR studies of C20 and, in particular, the identification of its isomers. 相似文献
12.
钛和氧之间存在多种成键方式,但迄今为止,二氧化钛团簇均只有少数几种异构体被报道. 与广泛使用的全局优化方法不同,本工作通过优化大量的随机初始结构,获得(TiO2)n (n=2-8)团簇稳定异构体. 首先利用PM6半经验方法对高达一万个以上的初始结构进行初步的优化筛选,并对筛选出的结构进行进一步的DFT计算以获得二氧化钛团簇的稳定异构体. 利用这种策略,发现了大量未经报道的稳定异构体,并提出了(TiO2)5和(TiO2)8新的最稳定异构体. 这些结构中包括含3个末端氧原子的异构体、含5配位氧原子和6配位钛原子的异构体等未经报道的新结构类型. 与丰富成键特征相对应,发现异构体数目随团簇尺寸的增大而急剧增加,对于(TiO2)7和(TiO2)8,能量在30 kcal/mol以内的异构体都在50个以上. 该工作发现了大量的二氧化钛小型团簇异构体,并凸显了其多样的结构特征,增进了对二氧化钛纳米团簇的结构、成键的理解,并为进一步的理论模拟、力场优化等提供了理论基础. 相似文献
13.
采用密度泛涵理论(density functional theory, DFT)中的广义梯度近似(generally gradient approximation, GGA)对富勒烯C72和内掺金属La富勒烯La2@C72三种同分异构体的几何结构和电子结构进行研究.发现在C72的三种同分异构体中,满足独立五边形规则(isolated-pentagon-rule,IPR)的C72(D6d<
关键词:
72')" href="#">C72
2@C72')" href="#">La2@C72
密度泛涵理论
几何结构
电子结构 相似文献
14.
15.
采用密度泛函理论中的广义梯度近似对Ni@C20H20的几何结构、成键和电磁性质进行密度泛函计算研究.结构优化发现位于偏离笼子中心三种位置处的Ni原子优化之后均回到笼子中心.结合能和能隙分析表明C20H20的中心位置是Ni原子热力学和动力学最稳定的位置.成键分析表明:Ni原子位于C20H20中心时,和C原子之间几乎没有相互作用,保持自己的孤立状态.电磁分析表明:原子磁矩为2关键词:
20H20')" href="#">C20H20
20H20')" href="#">Ni@C20H20
几何结构
成键
电磁性质
密度泛函理论 相似文献
16.
17.
Production, isolation, and characterization of group-2 metal-containing endohedral metallofullerenes
T. John S. Dennis H. Shinohara 《Applied Physics A: Materials Science & Processing》1998,66(3):243-247
80 , Ca/Sr/Ba@C82, Ca/Sr/Ba@C84) are investigated for the first time by UV-Vis-NIR absorption spectroscopy and high-resolution 13C NMR. Direct evidence of the endohedral nature and cage structures are revealed by these measurements. Furthermore, we have
found that each metallofullerene has 2–4 structural isomers, which have been isolated by multistage high-performance liquid
chromatography. These isomers have different cage structures and give characteristic UV-Vis-NIR absorption spectra.
Received: 22 September 1997/Accepted: 16 October 1997 相似文献
18.
V. Kumar 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):227-232
We report the recent findings of metal (M) encapsulated
clusters of silicon from computer experiments based on
ab initio total energy
calculations and a cage shrinkage and atom removal approach. Our
results show that using a guest atom, it is possible to wrap
silicon in fullerenelike (f)
structures, as sp2 bonding is not
favorable to produce empty cages unlike for carbon. Transition M
atoms have a strong bonding with the silicon cage that are
responsible for the compact structures. The size and structure
of the cage change from 14 to 20 Si atoms depending upon the
size and valence of the M atom. Fewer Si atoms lead to
relatively open structures. We find cubic,
f, Frank-Kasper (FK)
polyheral type, decahedral, icosahedral and hexagonal structures
for M@Sin with n = 12-16 and several different M
atoms. The magic behavior of 15 and 16 atom Si cages is in
agreement with experiments. The FK polyhedral cluster,
M@Si16 has an exceptionally large density
functional gap of about 2.35 eV calculated within the
generalized gradient approximation. It is likely to give rise to
visible luminescence in these clusters. The cluster-cluster
interaction is weak that makes such clusters attractive for
cluster assembled materials. Further studies to stabilize
Si20 cage with M = Zr, Ba, Sr, and Pb
show that in all cases there is a distortion of the
f cage. Similar studies on M
encapsulated germanium clusters show FK polyhedral and
decahedral isomers to be more favorable. Also perfect
icosahedral M@Ge12 and
M@Sn12 clusters have been obtained with
large gaps by doping with divalent M atoms. Recent results of
the H interaction with these clusters, hydrogenated silicon
fullerenes as well as assemblies of clusters such as nanowires
and nanotubes are briefly presented. 相似文献
19.
Various levels of calculations are carried out to explore the potential energy surfaces (PES) of singlet and triplet SiC3S, a molecule of potential interest in interstellar chemistry. At the DFT/B3LYP/6-311G(d) level, a total of 57 minimum isomers and 92 interconversion transition states are located. The structures of the most relevant isomers and transition states are further optimized at the QCISD/6-311G(d) level followed by CCSD(T)/6-311?+?G(2df) single-point energy calculations. At the QCISD level, the lowest-lying isomer is the chain-like SiCCCS 3 1 (0.0?kcal/mol) with a great kinetic stability of 54.1?kcal/mol. In addition, ring isomers CC-cCSSi 1 9 (19.8?kcal/mol), S-cCCCSi 1 12 (30.4?kcal/mol), S-cCCSiC 1 18 (9.4?kcal/mol), S-cSiCCC 1 21 (34.4?kcal/mol) and cage-like isomer cage-SiSCCC 1 23 (51.8?kcal/mol) also possess considerable kinetic stability (more than 10.0?kcal/mol). As a result, these six isomers are predicted to be possible candidates for future experimental and astrophysical detection. The bond natures and possible formation pathways in interstellar space of the SiCCCS are discussed. The predicted structure and spectroscopic properties for it are expected to be informative for the identification of SiC3S and even larger SiC n S species either in laboratory or in space. 相似文献
20.
Jerzy Moc 《Molecular physics》2013,111(20):3025-3035
Stationary points on the lowest singlet and triplet In2 + H2O potential energy surfaces (PESs) have been explored using the coupled cluster method, including single and double excitations with perturbative triples (CCSD(T)), and the density functional theory (DFT), employing the effective core potential (ECP) for indium (In), which accounts for scalar relativistic effects, with the triple-zeta quality basis set. The CCSD(T) calculated binding energy and anharmonic ν2-bending mode frequency for the triplet ground-state addition complex, In2… OH2(3B1), are consistent with the complex detected in the matrix isolation infrared (IR) spectroscopic study under the thermal conditions. The two minimum energy crossing points between the triplet and the singlet PESs that have been located between the structures of In2…OH2 and the transition state for the O–H bond breakage are not likely to be thermally accessible under the low-temperature matrix conditions. With the CCSD(T)-calculated In2 + H2O reaction profile and anharmonic vibrational frequencies for several In2(H)(OH) insertion product isomers, we support the IR matrix isolation detection (by two experimental groups) of the lowest energy singlet double-bridged In(μ-H)(μ-OH)In isomer. For the proposed two-step mechanism of H2 elimination from the In2(H)(OH) species, the estimated energy barriers are also compatible with experiment. 相似文献