分子基磁体Cr[N(CN)2]2电子结构和半金属性的第一性原理研究

基于第一性原理方法结合广义梯度近似,研究了分子基磁体Cr[N(CN)₂]₂的电子结构和半金属性. 对总能量,自旋极化的能带结构,态密度以及自旋磁矩的计算表明该分子磁体为半金属铁磁体．每个分子的总磁矩为2.00μB,其中Cr²⁺对分子磁矩的贡献较大,而配位体上的碳原子和氮原子的贡献相对较小．讨论了当晶格常数发生小幅变化时材料半金属性的变化.     

一维四元镜像对称光子晶体的帯隙研究

构造了由AsS、SiO2、PbTe和LiF四种介质组合而成的(AB)m(CD)m-1 A(DC)m-1(BA)m一维四元镜像对称结构光子晶体模型,利用传输矩阵法,研究了该结构的光学传输特性。结果表明:当m≥4,光线垂直入射时,在可见光全波段(400~760nm)范围内恰好有一严格帯隙。四介质的几何厚度各自独立递增时,帯隙红移,宽度增加,反之亦然。随着入射角增加,帯隙将产生蓝移。对于TE波,该光子晶体具有较好的角度宽容度,可实现全角度在可见光大部分波段(400~705nm)范围内的反射;对于TM波,仅能在可见光小部分波段(400~520nm)实现全角度反射。     

含复折射率介质一维准周期光子晶体的透射特性

用Si和复折射率介质构成了(AB)N型一维准周期光子晶体,在考虑Si色散关系的基础上,利用传输矩阵法研究了其透射特性.数值计算表明其TE波的透射谱有如下特征:电磁波垂直入射时,在相对频率0～4的范围内存在4个等间距的尖锐的透射主峰,各主峰低频端相距0.148 (ω/ω0)处都有一透射副峰.入射角增加,主峰的透射率下降,副峰的透射率上升.周期数N增加,各主、副峰位置都有蓝移,但主峰透射率逐渐减小,而各副峰的半峰全宽度变小.当两介质厚度为定值时,从第一主峰到第四主峰,其透射率依次减小,两介质厚度增加时,各主峰的透射率下降.复折射率虚部增加时,各透射峰的位置保持不变,主峰的透射率变大,而副峰的透射率变小,反之亦然.     

分子基磁体Cr[N(CN)2]2电子结构和半金属性的第一性原理研究

The electronic structure and half-metallicity of molecule-based ferromagnet Cr[N(CN)₂]₂ have been investigated using first-principles with generalized gradient approximation. The total energy, spin-polarized electronic band structure, density of states (DOSs) and spin mag-netic moments were all calculated. The calculations reveal that the compound Cr[N(CN)₂]₂ is a really half-metallic ferromagnet with a integral magnetic moment of 2.0000 μB per molecule in the optimized lattice constant. Based on the spin distribution and the DOS, it is found that the total magnetic moment is mainly from the Cr²⁺ with relative small contribution from C and N atoms. The sensitivity of the half-metallicity to small change in lattice constant is also discussed.     

含磁单负材料一维光子晶体的隧穿模特性

构造了由磁单负材料A、普通材料B( SiO2)和C(TiO2)组成的(AB)NC(BA)N型一维光子晶体,数值计算结果表明在3100～3700 nm的波长范围内出现了6个隧穿模.这些隧穿模有不同于传统缺陷模的特征:入射角θ、C介质层的位置、光子晶体的周期数N和A、B两层介质的几何厚度都不影响各隧穿模的位置.在θ＞46θ时,长波段的隧穿模消失.磁单负材料的介电常数变化,不影响隧穿模的个数和透射率.A、B两层介质的几何厚度变化量小于5;时,不影响各隧穿模的透射率,而C介质层的几何厚度对隧穿模的位置有影响.C介质层移动的单元数相同,隧穿模的变化也相同.     

Electronic and mechanical properties of half-metallic half-Heusler compounds CoCrZ(Z=S,Se, and Te)

The electronic structures, magnetic properties, half-metallicity, and mechanical properties of half-Heulser compounds CoCrZ(Z = S, Se, and Te) were investigated using first-principles calculations within generalized gradient approximation based on the density function theory. The half-Heusler compounds show half-metallic properties with a half-metallic gap of 0.15 eV for CoCrS, 0.10 eV for CoCrSe, and 0.31 eV for CoCrTe at equilibrium lattice constant, respectively. The total magnetic moments are 3.00μB per formula unit, which agrees well with the Slater-Pauling rule. The half-metallicity,elastic constants, bulk modulus, shear modulus, Pough's ratio, Frantesvich ratio, Young's modulus, Poisson's ratio, and Debye temperature at equilibrium lattice constant and versus lattice constants are reported for the first time. The results indicate that the half-Heulser compounds CoCrZ(Z = S, Se, and Te) maintain the perfect half-metallic and mechanical stability within the lattice constants range of 5.18-5.43  for CoCrS, 5.09-5.61  for CoCrSe, and 5.17-6.42  for CoCrTe,respectively.     

Quantum phase transition and Coulomb blockade effect in triangular quantum dots with interdot capacitive and tunnel couplings

The quantum phase transition and the electronic transport in a triangular quantum dot system are investigated using the numerical renormalization group method.We concentrate on the interplay between the interdot capacitive coupling V and the interdot tunnel coupling t.For small t,three dots form a local spin doublet.As t increases,due to the competition between V and t,there exist two first-order transitions with phase sequence spin-doublet-magnetic frustration phase-orbital spin singlet.When t is absent,the evolutions of the total charge on the dots and the linear conductance are of the typical Coulomb-blockade features with increasing gate voltage.While for sufficient t,the antiferromagnetic spin correlation between dots is enhanced,and the conductance is strongly suppressed for the bonding state is almost doubly occupied.     

含特异材料光子晶体隧穿模的偏振特性

构造了由普通材料A(SiO₂)和电单负材料B组成的(AB)^N(BA)^N型一维光子晶体.数值计算表明原禁带的1907.3 nm处出现了一个十分尖锐的隧穿模. 入射角增加,该隧穿模的透射率和半峰全宽度均保持不变,但位置发生蓝移, 入射角在15°-65°的区间内,移动率的绝对值 |dλ/dθ| 较大.当B介质的磁导率μ_B 从5增加到10时,只是隧穿模的位置发生了红移. 介质的几何厚度增加时,隧穿模的透射率不变,但其位置红移明显,半峰全宽略有增加.     

一种基于液晶光子晶体的可调谐滤波器

在由高纯硅和5CB液晶组成的光子晶体中,掺杂一装有电极的5CB液晶层作为调制层,由此构成了一可调滤波器.利用传输矩阵法计算了其透射谱,结果表明:控制调制层上电压有无,使调制层的折射率发生变化,就可以实现透射峰中心的移动,从而达到滤波波长可调的目的.该滤波器的结构周期以6至7为宜,且有一定的角度宽容性,特别适合小角度入射的情况.     

含左手材料的——维“啁啾”光子晶体的偏振特性

把“啁啾”函数引入含左手材料的一维光子晶体中,且左手材料的介电常数和磁导率采用Lossy Dryde model,利用传输矩阵法研究了其透射谱.结果表明:在“啁啾”函数对材料几何厚度调制较小时,该光子晶体有完整的禁带,随着调制的加强,禁带宽度增加,但底部逐步抬高.在相同的调制下,磁、电等离子体频率的比值越大,禁带宽度越宽.入射角增加,TE模的禁带宽度不变而TM模的禁带宽度变窄,TE模和TM模均产生了角度隙,此角度隙的宽度随入射角增加而变宽,且TM模的变化大于TE模的.周期数N变化时,角度隙基本不变.nR的变化对禁带和角度隙的位置没有影响,但nR越小,禁带底部越高且圆,角度隙中透射峰峰值越大.