Full-potential Linear-muffin-tin-orbital Molecular-dynamics Research Articles

First Principles Study on Sino (N=14-18) and Si10-Mom(M=1-8) Clusters

Combining the full-potential linear–muffin–tin–orbital molecular-dynamics (FP-LMTO-MD) and the Amsterdam Density Functional (ADF) with TZ2P basis set in conjunction with self-consistent-field (SCF), we have studied the geometric features and stabilities of the SinO (n=14-18) clusters.. The total binding energy Etot, gap of HOMO (highest-occupied molecular orbital)-LUMO (lowest-unoccupied molecular orbital) Eg, dipole moment μ and total constant volume heat capacity Cv(tot) were also calculated. The results show that the one dopant oxygen atom tends to occupy the edge or the surface position in the middle size silicon clusters (Sin, n=14-18). To further understanding the evolutionary tendency of the physical characteristics for the Si-O clusters with different composition, the Si10-mOm (m=1-8) clusters were also studied using the same methods. It was found that the structures of the Si10-mOm (m=1-8) clusters evolve from compact three dimensions to chain-like with increasing of the O proportion. The binding energy curve of Si10-mOm clusters with different m shows a dip at m=6, which suggests that an optimal proportion of O and Si atoms may exist in the Si10-mOm(m=1-8) clusters.

THEORETICAL STUDY OF NEUTRAL AND IONIC SinO(n = 1-13) CLUSTERS

A systematic theoretical study of the structural properties and stabilities for neutral Si n O (n = 1-13) clusters and their ions has been carried out using the full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method and the Amsterdam Density Functional (ADF) program with TZ2P basis set in conjunction with self-consistent field (SCF). Their ionization potentials (IPs), electron affinities (EAs), dipole moments μ, constant volume heat capacity Cv are computed. Based on the Mulliken population analyses, it is found that part of electronic charge is transferred from the Si atoms into the oxygen atom. Compared with other structures, the adsorption structures with an edge or a surface O atom are more stable. Calculations also show that the Si n O clusters with larger HOMO–LUMO gap exhibit high stability.

First-principles study on mixed Sin−1N (n=1–19) clusters

The mixed Si n −1 N ( n =2–19) clusters have been investigated systematically using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method and Amsterdam Density Functional (ADF) program with TZ2P basis set in conjunction with self-consistent field (SCF). Their ionization potentials (IPs), electron affinities (EAs), dipole moments μ , constant volume heat capacity per atom C v are computed. Based on the Mulliken population analyses, it is found that some of charge is transferred from the Si atoms into the nitrogen atom. Compared with other structures, most of the substitutional structures with three Si–N bonds are more stable. Our calculated results suggest that the N impurity atom improves the stability of the mixed clusters.

Theoretical study on the composition dependence of Ga 8−nAs n ( n=0–8) clusters

Using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method, we have investigated the dependence of GaAs clusters with eight atoms on composition. It is found that the ground state structures for Ga-rich and As-rich clusters are cube structures. As the ratio between gallium atoms and arsenic atoms is close to one, structural distortion become increasingly severe, or even the clusters adopt other geometrical configurations as their ground state structures. The energy gap E g between the highest-occupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO), and the vertical electron affinity show a certain degree of even/odd alternation with cluster composition. Among nine Ga 8− n As n ( n=0–8) clusters, only a few of clusters have different energy orders between the ionic and neutral isomers with large binding energy. Some ionic structures would change into other configurations due to severe structural distortion.

Geometric and energetic properties of Al-doped Si n ( n = 2–21) clusters: FP-LMTO-MD calculations

We have investigated the effect of aluminum impurity atoms on the geometric structures and stabilities of neutral and ionic Si n ( n = 2–21) clusters in detail by using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method. Our calculations suggest that most of the ground state structures for neutral and ionic Si n Al ( n = 1–20) clusters can be obtained by substituting one Si atom of their corresponding Si clusters with an Al atom. The neutral Si n –1Al clusters with one Al atom have similar geometrical configurations to those of the pure Si n clusters except for local structural distortion. But one Al impurity atom probably reverses the energy ordering of two isomers with small difference. Although, an Al heteroatom reduces the average binding energies for the mixed clusters, it would improve the bond strength between Si atoms in some mixed clusters. Our calculations also suggest that most of the ionic Si n –1Al clusters adopt the same geometrical configurations as their neutral clusters. But for one selected mixed cluster, the charged structures probably have different energy ordering from the neutral clusters. The anionic Si n –1Al − clusters, which are isoelectronic to their corresponding pure Si n clusters, show similar magic behavior.

Stability of carbon-doped silicon clusters: FP-LMTO molecular dynamics calculations

Using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method, we have investigated the effect of carbon heteroatom on the geometric structures and stability of Si n ( n = 2–19) clusters systematically. It has been found that one C atom does not change the geometrical configurations of the pure Si n clusters even though they undergo serious distortion, especially, for the smaller Si clusters. As the atom number increases, the influence of the C impurity atom would decrease. The C atom usually locates at the sites with more than three coordination in the most stable structures for the larger neutral Si n−1 C clusters ( n ≧ 6). It improves some bond strength, which increases the stability of some carbon-doped silicon clusters. On the other hand, the C heteroatom probably reverses the energy orderings of the Si clusters with small difference. Furthermore, their ionic geometric structures have been also investigated. Similarly, addition or removal of an electron does not change the geometrical configurations compared with those of their corresponding neutral clusters, but their energy orderings probably change.

Stable structures of neutral and ionic Ge n ( n=11–19) clusters

The lowest-energy structures of neutral and ionic Ge n ( n=11–19) clusters are obtained by using the full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method based on some genetic operations. We find a number of new ground state structures, which are more stable than those reported previously. Most of the lowest energy structures for the neutral and ionic Ge n ( n=11–19) clusters are obviously different from those of the corresponding Si n clusters although the geometrical configurations of the small clusters ( n<10) are basically the same. Our results also show that all the lowest energy structures of the cationic Ge n ( n=11–19) clusters have the similar geometrical configurations to those of the corresponding neutral Ge n ( n=11–19) clusters except for n=11. However, for the anionic Ge n ( n=11–19) clusters, the conclusion is almost the reverse. In addition, for the smaller clusters with n≤13, the polyhedral structures are more favorable, while the larger clusters from n=14 prefer the stacked structures. For the negative ions, their ground state structures transit from stacked structures into compacted structures at n=18.

Stable structures for Al 20 clusters

The low-lying energy structures of Al 20 cluster are obtained by full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method. A set of new low-lying energy structures including a new lowest energy structure, were found in our calculation. The waist-capped double icosahedral structure, which was considered as the global minimum previously, is merely one of the low-lying structures. Comparison and discussion between Al 20 and Si 20 have been made.

Structures ofAl19cluster: A full-potential LMTO molecular-dynamics study

Full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method have been performed to study the structures and energies of ${\mathrm{Al}}_{19}$ cluster. Besides the double icosahedral structure, which was considered to be the most stable structure of ${\mathrm{Al}}_{19}$ by early studies, a set of new isomers, the binding energies of which are a little bit larger than that of the double icosahedral structure in our calculation, are found. However, the energy differences between these isomers are so small that it is hard to take a single configuration as the ground-state of ${\mathrm{Al}}_{19}$ cluster.

Theoretical study of the adsorption of Si n[formula omitted] clusters on Si(100)– [formula omitted] surface

Using improved full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method, we have investigated the adsorption of free Si n clusters ( n = 5 – 7 ) on Si(100)– 2 × 1 surface. After adsorbed, the geometric configurations of the Si n clusters still remain although their structures have distorted significantly. Our calculations show that the cave site on the Si(100)– 2 × 1 surface is the most favorable adsorption site. The largest adsorption energy of the Si 5 cluster on it is 5.60 eV. The adsorption energies depend on the number of the chemical bonds between the clusters and the surface, the strength of the bonds, and the landing direction of the clusters. The investigations help us understand the microscopic mechanism of the deposition process of the Si n clusters on the Si(100)– 2 × 1 surface.

Stable structures of Ge n ( [formula omitted]) clusters

Using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method, we have investigated the geometric and electronic structures of neutral medium-sized Ge n ( n = 21 – 25 ) clusters. We have obtained not only all the low energy structures reported previously, but also some new structures with larger binding energies. Our calculations suggest that all the lowest energy structures are the stacked prolate structures including a tricapped trigonal prism (TTP) subunit at least. The structural characteristic is similar to that of the ground-state structures for Si clusters. However, the most stable structures for Ge and Si clusters are obviously different in the range 21–25.

Lowest energy structures of anionic Sin (n = 11–25) clusters

AbstractUsing full‐potential linear‐muffin‐tin‐orbital molecular‐dynamics (FP‐LMTO‐MD) method based on single‐parent evolution algorithm, we have studied the geometric and electronic structures of anionic Si11–25 clusters. For the anionic Sin (n = 11–20) clusters (except for n = 15 and n = 19), the ground state structures are in good agreement with the results obtained by using density functional theory with the gradient‐corrected functionals Perdew‐Wang‐Becke 88 (PWB). For n = 15 and 19, our results are in excellent agreement with those optimized using generalized gradient approximation (GGA) functionals based on single‐parent evolution method. In special, we have found the ground state structures for the anionic Si21–25 clusters using FP‐LMTO‐MD based on single‐parent evolution method. It is found that all the lowest energy structures include a sub‐unit of tricapped trigonal prism (TTP). Some lowest‐energy structures for the anions are different from those of neutrals. In addition, some energy orderings are also different by comparison with those of their corresponding neutral clusters. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Ground state structures of Si n ( n=11–25) clusters

Using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method based on single-parent evolution algorithm, we have investigated the geometric and electronic structures of neutral medium-sized Si n ( n=11–25) clusters. Some new isomers, which were not reported before, have been found. Some of them are essentially as stable as the corresponding ground state structures reported previously. Some of them are lower in energy than those reported before. Most of the most stable structures ( n=11–25) include a tricapped trigonal prism (TTP) at least. They would become prolate configurations as the atom number increases. Within the range of 11 to 25 atoms, the more compact cage-like geometries are not so stable as the prolate structures.

Electronic and geometric structures of Sin– and Sin+ (n = 2–10) clusters and in comparison with Sin

AbstractUsing full‐potential linear‐muffin‐tin‐orbital molecular‐dynamics (FP‐LMTO‐MD) method, we have studied the geometric and electronic structures of ionic Si2–10 clusters. The structures we obtained include not only all the most stable structures reported previously, but also some new structures. Our calculations show that the ground state structure of negative Si8– cluster ion is a new structure with C2v, which is different from that reported before. In addition, we have also found that the ground state structure of positive Si+10 cluster ion is a tricapped pentagonal bipyramid with Cs symmetry, which has been not reported previously. As for their electronic structures, these charged silicon clusters show 0.5–2.5 eV of energy gaps between the lowest unoccupied energy level and the highest occupied energy level. The gaps for cationic silicon clusters are closer to those of their corresponding neutral clusters, but many of the gaps for the anionic clusters are not.

Electronic and geometric structures of Ge n− and Ge n+ ( n=5–10) clusters in comparison with corresponding Si n ions

Using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method, we have studied the geometric and electronic structures of ionic Ge 5–10 clusters. Our calculations show that the ground state structures of some Ge cluster ions are different from those of their corresponding neutral Ge clusters. Furthermore, the positive Ge ions have more severe structural distortion than the negative Ge ions due to Jahn–Teller distortion. In addition, there are differences between the ground state structures of Ge ions and Si ions, although most of the Ge ions have similar geometrical configurations to their corresponding Si ions.

Stability of neutral and charged Si 50 cage and stacked structure and in comparison with Si 60 structures

We have performed calculations on the fullerene cage and stacked structures of neutral and ionic Si 50 cluster by full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method. It is found that the neutral and charged fullerene cages relax into distorted structures resembling puckered balls. Their electronic structures are remarkably similar besides their geometrical structures. However, the relaxed cages are still not so stable as the stacked structure built from tricapped trigonal prism. By comparison, for the fullerene cages and stacked structures of neutral and ionic Si 60 cluster, similar characteristics are found.

Distorted cage structures of Sin (n = 20, 24, 26, 28, 30, 32) clusters

We have performed calculations on the fullerene cage structures andthe binding energies of Sin (n = 20, 24, 26, 28, 30, 32) clustersby the full-potential linear-muffin-tin-orbital molecular dynamics(FP-LMTO-MD) method. It is found that the fullerene cages are notstable, and relax into structures which are severely distorted.Except for Si20, their atomic arrangement tendstowards tetrahedral geometry. After the structural distortion,about two silicon atoms can still be filled into the inside spacesof the distorted cages for Sin (n = 26-32).

Distorted cage structures of Si 36 cluster

Using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method, we have performed calculations on the fullerene cage structures and the binding energies of Si 36 cluster. It is found that their atomic arrangement tends towards tetrahedral geometry. The distorted structures are very stable. In addition, we have also investigated a stacked structure by tricapped trigonal prisms (TTP). The stacked structure is slightly more stable than the distorted fullerene cages. Their electronic states suggest that they present different electric properties.

Structures ofGenclusters(n=3–10)and comparisons toSinclusters

Full-potential linear muffin-tin orbital molecular-dynamics calculations have been performed to investigate the structures and energies of small ${\mathrm{Ge}}_{n}(n=3--10)$ clusters. To make a comparison between ${\mathrm{Ge}}_{n}$ and ${\mathrm{Si}}_{n},$ we have also investigated the structures and energies of ${\mathrm{Si}}_{n}(n=3--10)$ clusters. It is found that there is much in common between them. Their ground-state structures are about the same except for $n=8$ and $n=10.$ The potential barrier heights between some important structures have also been presented.

Twenty Six Stable Structures for Cluster Si10: A Full-Potential Linear-Muffin-Tin-Orbital Molecular-Dynamics Study

Using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method, we have performed calculations on twenty six structures for cluster Si 10 . Most of them are new structures. Its ground state structure (a tetracapped trigonal prism C 3v ) is in agreement with that ever put forth previously. Some of them are almost isoenergetic with the ground state structure.