A crystalline form of LiBC is known which has been predicted to be superconducting, with a Tc comparable to that of MgB_2. In both compounds, superconductivity is enhanced by the presence of two electronic bands, one of which is close to a dimensional crossover. Here, we take a quantum chemical approach, and investigate the structural and electronic properties of small clusters (LiBC)_n (n=1-4). With increasing cluster size, we find that several properties of crystalline LiBC evolve naturally from the corresponding properties of the clusters. In particular, one may recognize the origin of the solid bilayered structure, typical of magnesium diboride, and the character of the electronic sigma-band, arising from the overlap of the atomic orbitals in the in-plane BC rings. Two aspects especially emphasized are (a) the HOMO-LUMO gap as function of n and (b) the role of different spin multiplicity.
The effect of thermal shape fluctuations on the recurrent fluorescence of boron cluster cations, B$_N^+$ ($N=9-14$), has been investigated numerically, with a special emphasis on B$_{13}^+$. For this cluster, the electronic structures of the ground state and the four lowest electronically excited states were calculated using time-dependent density functional theory, and sampled on molecular dynamics trajectories of the cluster calculated at an experimentally relevant excitation energy. The sampled optical transition matrix elements for B$_{13}^+$ allowed to construct its emission spectrum from…
Structural and electronic properties of ternary clusters AlkTilNim, where k, l, and m are integers and k + l + m = 4 are investigated. These clusters are generated and studied by performing a two-stage density functional theory (DFT) calculations using the SWVN and B3LYP functional exchange correlations. In the first stage, an unbiased global search algorithm coupled with a DFT code with a light exchange-correlation and smaller basis sets are used to generate the lowest energy cluster structures. It is then followed by further optimization using another round of DFT calculation with heavy exch…
We present a comprehensive relativistic coupled cluster study of the electronic structures of the ThO and ThS molecules in the spinor basis. Specifically, we use the single-reference coupled cluster and the multi-reference Fock Space Coupled Cluster (FSCC) methods to model their ground and electronically-excited states. Two variants of the FSCC method have been investigated: (a) one where the electronic spectrum is obtained from sector (1,1) of the Fock space, and (b) another where the excited states come from the doubly attached electronic states to the doubly charged systems (ThO$^{2+}$ and …
Geometric, electronic and magnetic structure of Fe$_{x}$O$_{y}^{+}$ clusters
固体的几何形状、电子结构和磁性之间的相互关系既有趣又难以捉摸。这一点在小星系团中表现得尤为明显，那里出现了大量不寻常的结构。在这里，我们采用密度泛函理论结合遗传搜索算法，GGA $+U$和混合功能，以确定气相Fe $_{x}$ O $_{y}^{+/0}$集群的结构。对于Fe $_{x}$ O $_{y}$阳离子团簇，我们也计算了相应的振动光谱，并与实验进行了比较。我们成功地鉴定了Fe $_{3}$ O $_{4}^{+}$、Fe $_{4}$ O $_{5}^{+}$、Fe $_{4}$ O $_{6}^{+}$、Fe $_{5}$ O $_{7}^{+}$，并提出了Fe $_{6}$ O $_{8}^{+}$的结构。在Fe $_{3}$ O $_{4}^{+}$的三角形几何结构内，非共线的亚铁磁和铁磁态在能量上是可比的。Fe $_{4}$ O $_{5}^{+}$和Fe $_{4}$ O $_{6}^{+}$是亚铁磁性的，由于电离而具有1~ \muB{}的剩余磁矩。Fe $_{5}$ O $_{7}^{+}$是亚铁磁性的，因为Fe原子的数量是奇数。通过与块状磁铁矿的电子结构比较，发现Fe $_{4}$ O $_{5}^{+}$，Fe $_{4}$ O $_{6}^{+}$，Fe $_{6}$ O $_{8}^{+}$是混合价团簇.相反，在Fe $_{3}$ O $_{4}^{+…
Recently we have proposed an effective Hartree-Fock (EHF) theory for the electrons of the muonic molecules that is formally equivalent to the HF theory within the context of the Nuclear-Electronic Orbital theory [Phys. Chem. Chem. Phys. 20, 4466 (2018)]. In the present report we extend the muon-specific effective electronic structure theory beyond the EHF level by introducing the effective second order Muller-Plesset perturbation theory (EMP2) and the effective coupled-cluster theory at single and double excitation levels (ECCSD) as well as an improved version including perturbative triple exc…
Quantum Study of Dispersion-Corrected Electronic and Optical Properties of syn- and anti- B18H22 Clusters with/without Sulfur Doping for Tunable Optoelectronics
Damascus University（大马士革大学）；Higher Institute for Laser Research and Applications, Damascus University（大马士革大学激光研究与高等学院）；International University for Science and Technology（国际科学技术大学）；Antioch Syrian University（叙利亚安条克大学）
Vibrational and electronic absorption spectra calculated at the (time-dependent) density functional theory level for the bismuth carbide clusters Bi$_{n}$C$_{2n}$$^+$ ($3 \le n \le 9$) indicate significant differences in types of bonding that depend on cluster geometry. Analysis of the electronic charge densities of these clusters highlighted bonding trends consistent with the spectroscopic information. The combined data suggest that larger clusters ($n > 5$) are likely to be kinetically unstable in agreement with the cluster mass distribution obtained in gas-aggregation source experiments. Th…
