Overlap Population Research Articles

Molecular, spectroscopic, and magnetic properties of cobalt(II) complexes with heteroaromatic N(O)-donor ligands

New [Co(SCN)2(L)4/2] complexes, where L = β-pic (1), pyCH2OH (2), py(CH2)3OH (3), 1,2,4-triazolo[1,5-α]pyrimidine (4), [CoCl2(urotrop)2] (5), and [Co(DMIM)3]Cl2·H2O (6) where urotrop = hexamethylenetetramine and DMIM = 2,2′-bis(4,5-dimethylimidazolyl) were synthesized in simple reactions of CoCl2·6H2O with ammonia thiocyanate and pyridine type ligands or urotropine and diimidazolyl ligands with cobalt(II) chloride in methanol solutions. The orthorhombic crystallization for (1), (2), and (4), the monoclinic one for (3) and (5) as well as the hexagonal one for (6) were found. The plots of the overlap population density-of-states indicated nonbonding character of the interactions between pyridine derivatives ligands and cobalt(II) ions in the complexes (1)–(4). The electronic spectra showed almost perfect octahedral complex in the case of (6). The magnetic susceptibility measurements revealed paramagnetic behavior with low values of the Curie–Weiss temperature, positive for complex (5) and negative for the other ones, although the transition to collective magnetic state at low temperatures for (4) and (5) was evidenced by an observation of antiferromagnetic coupling with Neel temperature of 4.5 K and the ferromagnetic one with Curie temperature of 10 K, respectively.

The Alloying of Ti, C, N in Bulk -Fe and Their Effects on Bond Characters

The electronic structures and the bond characters of bulk -Fe with Ti, C, N additions are studied using the first-principls pseudopotential plane-wave method. The total energy and the cohesive energy are calculated, and the Mulliken population, the overlap population, the density of states and the charge density are also analyzed, which can give a microscopic reason why the mechanical property is improved after the infiltration of Ti, C, N into bulk Fe. The calculated results show that with the alloying element Ti(012.5 at%), C(011.11 at%), N(011.11 at%) contents increasing, the cohesive energy of alloy increases slowly and the structure keeps stable. The additions of Ti, C, N into the alloy enhance the reciprocal hybridization in Fermi energy level, and the binding abilities of Ti, C, N, Fe become stronger. The pseudo-gap near the Fermi energy level means the coexistence of covalent and metallic bonds in alloy. With the contents of alloying elements increasing, the covalent bondings between C, N and Ti, Fe become stronger, and part of C and N atoms will be bound to Ti atoms and form TiC and TiN particles, thereby strengthening the dispersion.

Simulating Electronic Structure of Condensed Adamantane

The condensed adamantane (C10H16) is the smallest member consisting of one diamond-structure-like used for lightemitting devices. We have simulated the electronic structure of C10H16 by discrete variational (DV)-Xα molecular orbital method. The 26(Td) high symmetries of C10H16 cluster models were designed by using 216 space group and used lattice parameter of diamond. The cluster models, radial function, energy levels, density of states, bond overlap and contour map were simulated and analyzed. It was found that the energy levels and density of states obtained the value of energy gap about of 6.25eV, agree with literature data. The bond overlap population has bonding and antibonding of atom interaction in cluster model and contour map of HOMO and LUMO.

A model for atomic hydrogen–bimetal interactions

The adsorption of atomic H on the bimetallic FeNi(111) surface has been studied by ASED-MO tight binding calculations. The energy of the system was calculated by the atom superposition and electron delocalization molecular orbital (ASED-MO) method. Seven H locations on the alloy surface were selected and the hydrogen atom was positioned in their energy minima configurations.By ASED-MO calculations, the H atom presents its most stable position when it bonds on top Fe atom at 1.5Å and, on bridge Fe–Fe at 0.7Å, respectively. In these cases, the strength of the local Fe–Fe bond decreases 12% and 33% of its original bulk value, respectively. As a consequence of Fe–H interaction, a decohesion mechanism in the Fe–Fe bond could be evidenced. On the other hand, the Fe–Ni and Ni–Ni superficial bonds are slightly modified between 0.4 and 2%. A discussion based on electronic structure studies using the concept of density of states (DOS) and crystal orbital overlap population (COOP) curves is presented.

Population analysis solution to hardness enhancement in TiCxN1−x

We investigated the hardness enhancement in titanium carbonitrides (TiCxN1−x) by the population analysis method based on first-principles calculations. Populations for bonds TiC and TiN in TiCxN1−x (0.25<x<0.75) are all positive. The enhanced hardness for titanium carbonitrides is well explained by overlap population analysis. Intrinsic hardness of TiCxN1−x has been calculated based on the obtained overlap populations. The calculated results are in good agreement with the available experimental data.

Adsorption of ammonia on vanadium–antimony mixed oxides

We analyzed the adsorption of ammonia (NH3) on the VSbO4(110) catalyst surface using density functional theory (DFT) calculations. We followed the evolution of the chemical bonds between different atoms of the resulting NH3/VSbO4 system and the changes in the electronic structure of the catalyst. NH3 preferential adsorption geometries were analyzed through the crystal orbital overlap population (COOP) concept and the density of states (DOS) curves. The VSbO4(110) surface exhibits Lewis and Brønsted acid sites on which the ammonia molecule can interact. On the Lewis acid site, NH3 adsorption resulted in the interaction between the N and a surface V-isolated cation. On Brønsted acid site, N interacted with a surface H coming from the chemical dissociation of water. The COOP analysis indicate that NH3 interaction on the VSbO4(110) surface is weak. In addition, the DOS curves show more developed electronic interactions for NH3 adsorption on Lewis acid site than over Brønsted acid site.

First-Principles Study on Mechanical Properties of IVB-Group Transition-Metal Nitrides TiN, ZrN, and HfN

IVB-group transition-metal nitrides are hot research materials due to their high hardness, good thermal stability, and excellent mechanical properties. In this paper, we studied the lattice parameters, elastic properties, electronic structures, and hardness of the face centered cubic TiN, ZrN, and HfN. The research shows that all the three types have excellent elastic properties. According to the result, elastic properties of HfN are the best of the three, as its bulk modulus and shear modulus are 278GPa and 240GPa respectively. With the calculation of electronic density of states, we find that all the three types are metallic. The wide pseudogap in DOS and the large overlap population indicate the strong Ti-N, Zr-N, and Hf-N bonds. The lower value of the density of states on the Fermi level shows that crystal structure of HfN is more stable. That is why the elastic properties of HfN are better than the others, mainly. The calculated hardness of TiN is 23.6GPa, which is the highest.

Structural, electronic properties and chemical bonding in protonated lithium metallates Li2−x H x MO3 (M = Ti, Zr, Sn)

Within density functional theory by an ab initio molecular dynamics method (SIESTA code) the features of structural, electronic properties and chemical bonding in lithium metallates Li2MO3 (M = Ti, Zr, Sn) are studied, as well as of their protonated forms Li2−xHxMO3 at all possible H+ → Li+ substitutions. With the use of the calculated crystal orbital overlap populations and the formation energies of Li2−xHxMO3 the most preferred H+ → Li+ substitutions in Li2MO3 metallates are discussed.

Density functional and bonding study of hydrogen and platinum adsorption on B2-FeTi (111) slab

We performed a density functional theory study (DFT) of hydrogen interaction with Pt on the B2-FeTi (111) surface. The DFT is employed to trace the relevant orbital interactions and to discuss the electronic changes of incorporating H on the Fe–Ti bonding. We determined the optimal location for Pt and then for adsorbed hydrogen. We also followed the density of states and the changes in the chemical bonding for both adsorbed atoms on the surface. The overlap population analysis reveals metal–metal bond breaking after hydrogen adsorption, being this bond the more affected.

First-Principles Study on Structure and Stability of YAP Crystal

The geometry optimization, formation energy, Mulliken populations, and density of states of YAP (YAlO3) crystal are studied by using first-principles method based on density functional theory. The optimal lattice parameters of YAP crystal are in good accordance with experimental results reported. The calculated formation energy (-3.73eV) indicates the excellent structural stability of YAP crystal. The obtained Mulliken charge populations of O, Al and Y atoms and their deviations from the formal ones, as well as overlap populations show YAP crystal is a mixed bond material with stronger ionic and weaker covalent bonds, which is attributed to the hybridization of atomic orbitals. The comprehensive effect of various interactions in the system makes YAP crystal more stable.

A theoretical study of the influence of dopants on the dehydrogenation properties of VH2

Using the plane wave ultrasoft pseudopotential method based on the first-principles density functional theory (DFT), the influence on the electronic structure and dehydrogenation properties of VH2 doped with Zr, Cu and Zn has been studied. The results show that the negative heat of formation increases and the valence electron number at the Fermi level EF, N(EF) decreases in the Zr-doped model, indicating the higher stability of VH2 after Zr alloying. On the other hand, the negative heat of formation of VH2 decreases and the N(EF) increases in Cu- or Zn-doped systems, suggesting the lower stability of VH2 after Cu or Zn alloying. The calculated overlap populations and electron densities of the V-H bond demonstrate that the bonding is strengthened by Zr doping and weakened by Cu or Zn doping. The results predict that the maximum capacity to absorb and desorb hydrogen can be raised by the introduction of Zr and reduced by the introduction of Cu or Zn, while the dehydrogenation properties will be poorer in Zr-doped systems and enhanced in Cu- or Zn-doped systems. These predictions are consistent with the experimental results. Mulliken populations were also calculated and it was found that the Mulliken population of the V 3d orbitals decreased as a result of Zr doping, and increased after Cu or Zn doping.

Electronic structure and absorption spectra of yttrium quinaldinates with an island and polymer structure

The electronic absorption spectra and electronic structure of yttrium quinaldinates with an island and polymer structure were studied. A comparative analysis of the energies of the singlet and triplet excited states, the total energies of complex compounds in the ground state, and Mulliken’s bond overlap populations was performed by the TD-DFT method with the B3LYP density functional. For yttrium quinaldinate with a polymer structure, the distance between the highest occupied and lowest unoccupied orbitals was found to be longer than for the compound with an island structure. The transition energies were shifted to the blue region, which accounts for the higher stability of the polymer compound.

Adsorption of NH 3 and NO 2 molecules on C 48B 6N 6 heterofullerene: A DFT study on electronic properties

Adsorption of NH 3 and NO 2 molecules on the external surface of C 48B 6N 6 heterofullerene is investigated using DFT method. Attachment of NH 3 and NO 2 on C 48B 6N 6 heterofullerenes are compared with the bare C 48B 6N 6 model optimized at the B3LYP/6-31G ⁎ level. The high surface binding energies indicates that ammonia undergoes chemical adsorption and could be compatible with the long recovery time but C 48B 6N 6 should be good NO 2 sensors with quick response as well as short recovery time. Total (TDOS) and partial (PDOS) density of state calculations is also considered to elucidate the difference in the NH 3 and NO 2 gas detection mechanism of C 48B 6N 6. The overlap population density of state (OPDOS) indicated that the chemical adsorption is due to the overlap of atomic orbitals below the Fermi level. The calculated results suggest that the C 48B 6N 6 heterofullerene is a suitable sensor material for NO 2 and is an ideal material for elimination and filtering of ammonia.

Surface Effect and Band-Gap Oscillation of TiO2 Nanowires and Nanotubes

We have presented a comprehensive investigation for the geometric, energetic, and electronic structures of the rutile TiO2 nanowire (NW) and nanotube (NT) by the first-principles calculations accompanied with the crystal orbital overlap population and the wave function analysis. Taking into account the surface interactions, we found that the geometry and stability of TiO2 NWs and NTs greatly depend on the surface structure with the size decreasing, which demonstrates the forming shape and structure. The competition between the surface-bonding effect and the quantum-confinement effect induces the oscillation behavior and the direct–indirect transition of the band gap of TiO2 NWs and NTs. These findings not only provide a new insight into the fundamental understanding of TiO2 nanostructures but also provide useful information to design TiO2 nanostructures for different applications.

Interaction of hydrogen and platinum over a B2 FeTi (110) Slab

In this work, we present a density functional theory (DFT) study of hydrogen interaction with Pt on a B2 FeTi (110) metallic surface. DFT is used to trace relevant orbital interactions and to discuss the electronic consequences of incorporating H on Fe–Ti bonding. We determined the optimal location for Pt and, then, for adsorbed hydrogen. In addition, we followed the density of states and changes in chemical bonding both in the surface and the adsorbates. The overlap population analysis reveals metal–metal bond breaking after hydrogen adsorption, thus being the inter-metallic bond the most affected one.

Oxygen adsorption on Al (111) surface interstitial site calculated by density functional theory

AbstractThe adsorption possibilities of oxygen atoms at Al (111) surface for different oxygen atom coverages (Θ) from 0.25 to 1 ml have been studied using first principles based on density functional theory with generalized gradient approximation. The results show that the interstitial sites on Al (111) surface are relatively stable, in which binding energies are 0.6 ∼ 1 eV/atom lower than those on surface face centered cubic (fcc) sites for the different coverages. The binding energy and work function of the oxygen‐adsorbed surface increase with the oxygen atom coverage. Moreover, the oxygen atom at one tetrahedral site of Al (111) subsurface becomes more and more unstable with the decrease of the coverage, and it moves up to the Al (111) surface hexagonal close packed (hcp) site at Θ = 0.25. All the octahedral absorption sites are also unstable in relatively lower coverages (Θ = 0.5 and 0.25). The bond length and overlap population between Al and O, including the relaxation effects on the oxygen atom coverage are discussed. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Electronic and geometric structure of the protonated forms of nickel β-diketonates

The effect of protonation on the electronic and spatial structure of nickel malonodialdehynate Ni(Mal)2 and acetylacetonate Ni(Acac)2 were studied by quantum chemical density functional theory (DFT) method. The metal ring geometry, the energies and the composition of molecular orbitals (MO), the effective charges on atoms, and the total overlap populations were determined, and the possible proton location sites were identified. The variation of the MO energy depending on the electron density distribution on the protonated and non-protonated ligands was considered. Proton addition to one of the oxygen atoms was shown to be most likely.

YbOs4Sb12 Filled Skutterudite: Its Electronic Properties

A theoretical calculation on YbOs4Sb12 filled skutterudite is reported. The calculated energy bands yield indication of a semimetallic behavior, while the projected density of states provide support for the existence of hybridization formed by Yb f-, Os d-, and Sb p-states. From the analysis of the energy bands that crosses the E f, it is possible to infer a high effective mass; this value is added to the existence of a strong hybridization yielded indication of the heavy Fermion behavior for this compound which agrees with the experimental information available. The absence of a minigap provides an indication that this compound is not likely to serve as a good thermoelectric material, unless doped in a certain direction as to enhance the probability to open the necessary minigap between the valence and conduction bands. Crystal orbital overlap population analysis yielded indication for the absence of a ferromagnetic instability.

Density functional theory study of selenium adsorption on Fe(1 1 0)

The adsorption of atomic Se on a Fe(1 1 0) surface is examined using the density functional theory (DFT). Selenium is adsorbed in high-symmetry adsorption sites: the -short and long-bridge, and atop sites at 1/2, 1/4, and 1 monolayer (ML) coverages. The long bridge (LB) site is found to be the most stable, followed by the short bridge (SB) and top sites (T). The following overlayer structures were examined, p(2 × 2), c(2 × 2), and p(1 × 1), which correspond to 1/4 ML, 1/2 ML, and 1 ML respectively. Adsorption energy is −5.23 eV at 1/4 ML. Se adsorption results in surface reconstruction, being more extensive for adsorption in the long bridge site at 1/2 ML, with vertical displacements between +8.63 and −6.69% -with regard to the original Fe position-, affecting the 1st and 2nd neighbours. The largest displacement in x or y-directions was determined to be 0.011, 0.030, and 0.021 Å for atop and bridge sites. Comparisons between Se-adsorbed and pure Fe surfaces revealed reductions in the magnetic moments of surface-layer Fe atoms in the vicinity of the Se. At the long bridge site, the presence of Se causes a decrease in the surface Fe d-orbital density of states between 4 and 5 eV below Fermi level. The density of states present a contribution of Se states at −3.1 eV and −12.9 eV. stabilized after adsorption. The Fe–Fe overlap population decrease and a Fe–Se bond are formed at the expense of the metallic bond.

Investigation of the (√3 × √3)R30°-Cu 2Si/Cu(1 1 1) surface alloy using DFT

The electronic structure of the FCC, HCP and 2-fold bridge phases of the (√3 × √3)R30°-Cu 2Si/Cu(1 1 1) surface alloy have been investigated using LCAO-DFT. Analysis of the total electron density, partial density-of-states (PDOS) and crystal orbital overlap population (COOP) curves for the system have shown a surprising similarity between the intra- and inter-layer Si–Cu bond for each phase. Low hybridization between the Si 3s and 3p orbitals results in a low directionality of the Si–Cu bond within each of phase. The Si 3s orbitals are shown to form covalent bonds with their surrounding Cu atoms whereas the Si 3p and 3d orbitals are shown to form combinations of covalent and metallic bonds. The Si–Cu interaction is shown clearly to extend to the second layer of the alloy in deference to previous studies of Si/Cu alloys.