NO adsorption and dissociation on subnanometer Pdn (n = 8, 13, 19, 25) clusters were first studied with GGA-DFT. The transition structures of the NO dissociating on the potential-energy surfaces were derived using the climbing image nudged-elastic-band (CI-NEB) method. The preferred NO adsorption positions are bridge sites on Pdn (n = 8, 19) and hollow sites on Pdn (n = 13, 25). The NO adsorption energy values on hollow sites of icosahedron-based Pdn (n = 13, 25) are relatively higher than that on the bridge site of octahedral Pd19. However, the NO dissociation barrier on octahedral Pd19 is lower than that on icosahedron-based Pdn (n = 13, 25) clusters. These results suggest on a Pdn (n = 8, 13, 19, 25) scale the NO activity may no longer rely on the cluster size but rather on the geometric structure of Pdn clusters. The coordination number of the NO adsorption site is found to be the key factor to determine the structure sensitivity of NO adsorption and dissociation. The charge difference and Hirshfeld charges reveal that the charge transfer is from the Pdn clusters to NO and increases upon NO dissociation. PDOS reveals that the 3σ, 4σ, 5σ, 1π, and 2π peaks of NO are sensitive not to Pdn cluster size but to NO adsorption sites. Our calculations may provide an insight into structure-sensitive Pd-based catalysts for NO removal on a subnanometer scale.

The Pd-catalyzed dearomatization of naphthalene allyl chloride with allyltributylstannane has been investigated using density functional theory (DFT) calculations at the B3LYP level. The calculations indicate that the (ŋ1-allyl)(ŋ3-allyl)Pd(PH3) complex is responsible for the formation of ortho-dearomatized product. Moreover it is easy to produce the ortho-dearomatized product when reductive elimination starts from (ŋ3-allylnaphthalene)(ŋ1-allyl)Pd complex 7, while it is easy to form the para-dearomatized product when reductive elimination starts from (ŋ3-allylnaphthalene)(ŋ1-allyl)Pd complex 9. The Stille coupling products can’t be produced due to high reaction energy barrier.

•The Pdn cluster size effects on the adsorption–dissociation and the electronic properties.•|Ead| decrease from 0.81, 0.67, 0.64 to 0.45 eV on Pdn (n = 4, 6, 13, 19), and increase to 0.51 eV for Pd55.•ΔE# decrease from 0.41, 0.40 to 0.058 eV on Pdn (n = 4, 6, 13), and increase to 0.18 and 0.20 eV on n = 19, 55.•H2 dissociation is more favorable than desorption and Pd13 is the most activated cluster.•Charge-transfer from Pdn to H2 increases, and s-band of H2 shifts to Ef upon H2 dissociation.The H2 adsorption and dissociation on Pdn (n = 4, 6, 13, 19, 55) clusters were studied with GGA-DFT. The heat releases decrease from 0.81, 0.67, 0.64 to 0.45 eV for the H2 adsorbed on the Pdn (n = 4, 6, 13, 19), and increase to 0.51 eV on the Pd55. Energy barriers of the H2 dissociation decrease from 0.41, 0.40 to 0.058 eV on the Pdn (n = 4, 6, 13) and increase to 0.18 and 0.20 eV on the Pdn (n = 19, 55). Comparing the adsorption heats with energy barriers, the H2 dissociation is energetically favorable. The Hirshfeld charge reveals that charge-transfer from Pdn to H2 increases upon adsorption–dissociation. The PDOS shows that the s-band of H2 shifts toward Fermi level and d-band of the Pd4–2H complexes is more delocalized upon H2 dissociation. Present results show a structure sensitivity of the H2 adsorption–dissociation on the Pdn clusters due to inherent size changes.

Excited state hydrogen-bonding dynamics of coumarin in ethanol solvent has been studied using TDDFT/6-311++G(d,p) and a conductor-like polarizable continuum model. The geometry, hydrogen bond binding energy and frequency analysis indicate that the intermolecular hydrogen bond between C102 and ethanol is strengthened in the excited state. The binding energy is increased from 27.81 kJ mol−1 in the ground state to 32.36 kJ mol−1 in the S1 state. The CO and O–H stretching bands in C102–EtOH are strongly red-shifted due to the formation of the intermolecular hydrogen bond. In the excited state, redshift occurs for the CO and O–H in the C102–EtOH complex. The excitation energy and frontier molecular orbital analysis indicate that S1 of the C102–EtOH complex is the locally excited state. S1 corresponds to the orbital transition from the HOMO to the LUMO with the ππ* character. Furthermore, the internal conversion from the excited to ground state is enhanced by hydrogen bond strengthening.

•Intermolecular hydrogen bond is strengthened upon ICT photoexcitation.•The experimental UV absorption peak at 346 nm is the S1 with ππ* electron transfer.•The internal conversion rate of HCMI can be tuned by the hydrogen bonding.•Intramolecular electron transfer occurs from OH to C8CF3 upon ICT excitation.The excited hydrogen bonding between hydroxy coumarin (HC) and hydroxy coumarin/methyl imidazole (HCMI) has been studied using TDDFT method. The intermolecular hydrogen bond OH⋯NH is strengthened upon intramolecular electron transfer (ICT) excitation. The calculated ultraviolet absorption spectrum is in good agreement with the experimental data, and the experimental peak at 310 nm is predicted to be the excited S1 state. From the frontier molecular orbitals of HCMI, the HOMO and the LUMO are of π and π* character and the transition from the ground state to the S1 state is a local exciting process. The intramolecular electron transfer of π electron from the OH group to an π* orbital of C8CF3 group not to CO group is found upon ICT excitation. The calculated gap between HOMO and LUMO shows that HCMI can be more easily excited than free HC. The hydrogen bonding can modulate the internal conversion rate of HCMI.

The structural evolution and competition between the hollow cage, amorphous, fcc-like and tubular structures for medium-sized Aun (n = 29–35) clusters were investigated using density functional theory combined with empirical genetic algorithm search. Aun (n = 29–32) clusters prefer the hollow cage structures. Amorphous core–shell configurations prevail over other kinds of structural motifs for Aun (n = 33–35). A transition from hollow cage to amorphous packing occurs at n = 33. The size-dependent HOMO–LUMO gap, vertical ionization potential and electron density of states were discussed to illustrate the relationship between the electronic properties and the geometry structures.Highlights► An extensive approach to explore the potential energy surface. ► A structural transition from hollow cage to amorphous geometry occurs at the Au33. ► The electronic properties show sensitivity to hollow cage and amorphous geometry.

Low-lying structures and structural evolution of Ptn (n = 15–24) clusters were studied using a genetic algorithm followed by local optimization with density functional theory calculations. As a whole, the lowest energy structures of Ptn (n = 15–24) clusters are likely to form open structural motifs not the atomic closed shell structures. Four kinds of structural motifs, i.e., dodecahedron based (DODB), cuboctahedron based (COB), layered triangular (LT) and cubic configurations have been investigated for the medium-sized Ptn (n = 15–24) clusters. The Ptn (n = 15–16, 19, 24) prefer the DODB growth pattern. While the Ptn (n = 17–18, 20) lean to the LT configuration. The lowest energy structures of Pt21 and Pt23 clusters adopt the cubic structure. Ptn clusters at n = 15, 18, 24 are relatively more stable and these clusters are “magic” numbered. Three different spin multiplicities (M = 1, 3 and 5) have been examined for Ptn (n = 15–24) clusters, and found that the most stable Pt22 cluster is the only one in triplet state. These results are significantly different from those predicted in earlier works. The relationship between electronic property and geometry was also discussed.

Structural evolution of Agnv(v=±1,0;n=3–14) clusters have been studied using an extensive, unbiased search based on genetic algorithm and density functional theory (DFT) methods. Cationic, neutral, and anionic silver clusters have planar shapes for their lowest-energy structures up to n = 7, 6, and 6, respectively. Most of the competitive candidates for Agnv(v=±1,0;n=9–14) are found to adopt close-flat configurations. The present results obtained by employing the Perdew–Wang 91 (PW91) exchange-correlation functional are significantly different from those predicted in earlier work using empirical and semi-empirical potentials, and partly in line with the previous first-principles calculations. The dependences of the lowest-energy structures of Agnv(v=±1,0;n=3–14) on second finite differences of total energy, binding energies per atom, highest occupied and lowest unoccupied molecular orbital energy gaps, ionization potentials, and electron affinities are studied in detail. The calculated ionization potentials and electron affinities of the optimal clusters display distinct even–odd oscillations. The neutral Ag clusters with 6-, 8-, and 14-atoms are suggested to be “magic” clusters by an analysis of their geometric and electronic properties.

Using a genetic algorithm followed by local optimization with density functional theory, the lowest-energy structures of Agn clusters in a size range of n=3–22n=3–22 were studied. The Agn (n=9–16n=9–16) clusters prefer compact structures of flat shape, while the Agn(n=19,21,22) clusters adopt amorphous packing based on a 13-atom icosahedral core. For Ag16, two competitive candidates for the lowest-energy structures, namely a hollow-cage structure and close-packed structures of flat shape, were found. Two competing candidates were found for Ag17 and Ag18: hollow-cage structures versus icosahedron-based compact structures. The lowest-energy structure of Ag20 is a highly symmetric tetrahedron with TdTd symmetry. These results are significantly different from those predicted in earlier works using empirical methods. The ionization potentials and electron affinities for the lowest-energy structures of Agn (n=3–22n=3–22) clusters were computed and compared with experimental values.

Using a genetic algorithm followed by local optimization with density functional theory, the lowest-energy structures of Agn clusters in a size range of n=3–22 were studied. The Agn (n=9–16) clusters prefer compact structures of flat shape, while the Agn(n=19,21,22) clusters adopt amorphous packing based on a 13-atom icosahedral core. For Ag16, two competitive candidates for the lowest-energy structures, namely a hollow-cage structure and close-packed structures of flat shape, were found. Two competing candidates were found for Ag17 and Ag18: hollow-cage structures versus icosahedron-based compact structures. The lowest-energy structure of Ag20 is a highly symmetric tetrahedron with Td symmetry. These results are significantly different from those predicted in earlier works using empirical methods. The ionization potentials and electron affinities for the lowest-energy structures of Agn (n=3–22) clusters were computed and compared with experimental values.