5-step algorithm to accelerate the prediction of [Au25(SR)19] z clusters (z = 1-, 0, 1+).

Prediction of the structure of thiolated gold clusters is time demanding, and new strategies are needed to expedite this process. In this study, using one five-step algorithm and dispersion corrected density functional theory (DFT-D) calculations, new models are proposed for neutral and charged Au25(SR)19 clusters that contain one extra ligand with respect to the ubiquitous Au25(SR)18 cluster. The algorithm counts for constituting tetrahedra/octahedra units of related isomers, and it provides their energy order. In general, one structure comprising one Au11 inner core is found as energy minima of neutral and charged Au25(SR)19 clusters. Therefore, our new neutral structure is 0.20 eV (-CH3 and TPSS) more stable than the previously reported one. With respect to neutral and anionic structures containing inner cores with C 2v symmetry, ultraviolet-visible/circular dichroism profiles are similar.

On the structure of Au11(SR)9 and Au13(SR)11 clusters.

Thiolated gold clusters are constituted by building blocks (Au4, Au6, Au12 and so on) and protected by staple motifs (-S-Au-S-Au-S-…). In this study, we propose the structure of Au11(SR)9 and Au13(SR)11 clusters that are in the synthesis route of the ubiquitous Au15(SR)13 cluster. Our DFT-D calculations support one triangular Au3 unit as the smallest one comprising the structure of the Au11(SR)9 cluster, while it competes with the Au4 unit found in the Au13(SR)11 cluster. The ligand effects on the electronic, optical and chiroptical properties were studied by considering H, CH3, phenyl and adamantyl as protecting ligands. In the case of the Au11(SR)9 cluster, its Au3 inner core is protected by one dimer motif and one [Au6(SR)6] cyclomer when H and CH3 were considered as ligands, and the preference for Au3 over Au4 inner core was calculated to be 0.042 (H), 0.190 (CH3), and 0.117 eV (adamantyl). In contrast, the preference for one Au4 core increased when using phenyl ligands (0.23 eV energy difference) and dimer and pentamer motifs. Moreover, the Au13(SR)11 cluster (R = CH3) has one Au4 inner core and is protected by the combination of cyclomer, monomer and dimer motifs, and the isomer containing one Au3 inner core and protected by one tetramer and one [Au6(SR)6] cyclomer is 0.170 eV less stable. This implies that the Au3 unit is important in these small sizes and that the energetic preference depends on the used ligand types. Moreover, we discuss the IR/Raman, optical absorption (UV-vis), and circular dichroism (CD) spectra of our predicted new structures.

Effect of the charge state on the structure of the Au60 cluster.

This manuscript outlines a DFT-D study of a neutral and charged Au60 cluster. The neutral structure features an I-symmetry, while 1-, 1+, and 2+ charge states result in a structure with Cs symmetry. The main difference among neutral and charged clusters is their compactness and we used a polyhedral approach to analyze their structure in terms of tetrahedral and octahedral building blocks. Moreover, we calculated their IR/Raman spectra to distinguish among them.

Effect of the charge state on bare monoicosahedral [Au13]z+ and diphosphine-protected Au13 clusters [Au13(dmpe)5Cl2]z+: structural, electronic and vibrational DFT studies.

In this paper a GGA-PBE study of [Au13]z+ bare clusters (z = +3, +5) and diphosphine protected [Au13(dmpe)5Cl2]z+ clusters (z = 1, 3) is presented. To explore the application of the [Au13((P(CH3)2CH2)2)5Cl2]3+ cluster as a cisplatin carrier, we have evaluated the adsorption energy of one cisplatin dimer interacting with the complex (0.53 eV). By considering a 1+ charge state, we have determined one cluster featuring a slight reduced HOMO-LUMO gap, with an inner Au13 core heavily distorted (strong charge effects). It is found that the filling/distribution of the superatomic energy levels is affected by the addition of two electrons to the [Au13(dmpe)5Cl2]3+ cluster with a reduction of its symmetry (C1 point group). In addition, the calculated IR and Raman spectra of charged [Au13(dmpe)5Cl2]z+ clusters allow distinguishing them.

New two-dimensional carbon nitride allotrope with 1 : 1 stoichiometry featuring spine-like structures: a structural and electronic DFT-D study.

In this communication the prediction of a two-dimensional carbon nitride allotrope (CN) featuring a 1 : 1 stoichiometry is considered. Calculations were carried out under ambient conditions of pressure and temperature (1 atm, 300 K), to prove its dynamic (phonon) and thermal stability. The novel CN structure contains pentagonal rings (c-C3N2) linked by nitrogen atoms, and separated by holes, whereas the sp3-like C atoms are bonded to isocyano (C[triple bond, length as m-dash]N-) groups projecting out of its surface and resembling spine-like formations. The predicted structure has a calculated indirect bandgap of approximately 2.78 eV (hybrid HSE06 approximation), that is in the range of visible light, and this it might increase its use in the field of photocatalysis.

Hydrogen storage on volleyballene.

This study is devoted to the hydrogenation of the recently predicted volleyballene (Sc20C60) compound. The hydrogenation produces structures with 24 and 70 H atoms, respectively. Twelve of the 20 available Sc atoms and C5 rings are found as preferred sites for hydrogenation. DFT calculations attest a H2 uptake capacity of 4.20 wt% for the heavily hydrogenated structure (Sc20C60H70), and a corrected -0.11 eV/H2 adsorption energy value. Calculated entalphy (negative) and entropy (positive) values assure that the hydrogenation reaction of volleyballene can be achieved at ambient temperature. The heavily hydrogenated structure holds a 1.1 eV HOMO-LUMO gap value and it does not feature imaginary frequencies attesting its experimental convenience.

Study of the interaction between cisplatin and the Au18(SR)14 cluster: in search of an appropriate cisplatin carrier.

Cisplatin is a well known anti-cancer drug and considered as essential by the World Health Organization. However, cisplatin features side effects during medical treatments due to its lack of selectivity resulting in the indiscriminate death of cells including healthy cells. To solve this issue, it is mandatory to improve its delivery towards affected organs or tissues. The well known bio-compatibility of gold clusters encouraged us to study the interaction between cisplatin molecules and the Au18(SR)14 cluster (named Au18) and our DFT calculations have provided insight into this aspect. Calculated adsorption energy values of the cisplatinn/Au18 complexes are within the 0.5-3.6 eV range, which attests to their unique interaction. In addition, their calculated optical absorption (UV-vis) and circular dichroism (CD) spectra display distinct peaks in such a manner that UV/CD spectra can be used as fingerprints by experimentalists.

Doped penta-graphene and hydrogenation of its related structures: a structural and electronic DFT-D study.

The structure of penta-graphene (penta-C), an irregular pentagonal two-dimensional (2D) structure, has been predicted recently. In this communication we carried out a dispersion-corrected density functional theory (DFT-D) study of the penta-C doped with Si, Ge and Sn atoms and its related hydrogenated penta-C structures (H-penta-C-X). We predict various new structures as thermally stable based on Born-Oppenheimer molecular dynamics (BOMD) calculations. Moreover, their dynamical stability is attested by phonon dispersions spectra. In general, we found that the bandgap value of doped structures reduces, while H-penta-C-X show large bandgap values. This feature can be exploited for potential uses of hydrogenated doped-penta-C structures as dielectric layers in electronic devices.

New insight into the structure of the C60Sc20 cluster: bonding, vibrational and optical properties.

Recently, a new stable C60Sc20 cluster has been proposed. Its structure has Th symmetry and a large HOMO-LUMO gap value. In this communication a systematic study of its bonding, IR, Raman and absorption spectra has been carried out. Its calculated absorption spectrum features four peaks located at 1.34, 1.6, 1.87 and 2.1 eV. Moreover its Raman and IR spectra are dominated by the signals of normal modes with Tu, Eg and Au irreducible representations.

Chiral phosphorus nanotubes: structure, bonding, and electronic properties.

The study of black phosphorus nanotubes (PNTs) had been devoted to zigzag and armchair structures, with no consideration of chiral structures to date. In this communication, we studied the structural and electronic (band structure) properties of chiral nanotubes using a periodic plane wave-pseudopotential approach. We found that some chiral nanotubes display similar bandgaps and binding energies per atom (BEA) as armchair PNTs and Born-Oppenheimer molecular dynamics (BOMD) calculations attest their thermal stability. Interestingly, we determined that the bandgap is tuned by varying the PNTs chirality and it is not related to their diameters. This feature can be exploited in optical and electronic applications wherein a direct and sizable bandgap is required.

New insight into the structure of thiolated gold clusters: a structural prediction of the Au187(SR)68 cluster.

The structure of the thiolated Au187 cluster has been elucidated by density functional theory calculations. The structural model comprises a Marks-decahedral Au153 core protected with 34 monomer motifs. The predicted structure accomplished in this study is in good agreement with the experimental X-ray diffraction pattern. It is noteworthy that the used methodology represents an advance in the prediction of the molecular structure of thiolated gold clusters constituted by hundreds of gold atoms.