First principles studies on the growth of small Cu clusters and the dissociative chemisorption ofH2

Abstract

The sequential growth of small copper clusters up to 15 atoms and the dissociative chemisorption of H 2 on the minimum energy clusters are studied systematically using density functional theory under the generalized gradient approximation. We found that small Cu n clusters grow by adopting a triangular growth pathway. The pentagon bipyramid structural arrangements are strongly favored energetically in the growth and the new addition in the cluster occurs preferably at a site where the atom is capable of interacting with more adjacent atoms. To understand the evolution of small copper clusters, we also performed calculations on selected icosahedral clusters ͑for n = 13, 19, 25, 55͒ and fcc-like clusters ͑n = 14, 23, 32, 41͒. By extrapolating/ interpolating the binding energies of triangular clusters, icosahedral clusters, and bulk-like clusters, we found that structural transitions from the triangular growth clusters to the icosahedral and fcc-like clusters occur at approximately n = 16 and n = 32, respectively. Subsequently, we performed extensive calculations on the dissociative chemisorption of H 2 on the minimum energy clusters. The chemisorption likely occurs near the most acute metal site with the two H atoms residing on the edges, which differs significantly from the chemisorption on Cu surfaces that usually takes place at the hollow sites.

IR Spectroscopic Characterization of H2 Adsorption on Cationic Cun+ (n = 4–7) Clusters

“…All of the local minima structures obtained from these MH runs for each size are carefully refined by environment descriptors 42 implemented in the FLAME code 43 to conveniently identify and remove potential duplicates. This way, we find all of the structures which have been reported before by Guvelioglu et al 21 In addition, we also discover several new low-energy structures for each cluster size.…”

“…Although we cannot completely rule out to have missed a relevant structure for [7Cu, 2H/2D] + , we consider our global sampling for this like for all other cluster sizes to be rather extensive—given the fact that we have automatically found all of the minima structures that Cheng and co-workers have constructed manually for H 2 adsorption on neutral Cu 7 clusters. 20 , 21 Instead, future work needs to show whether the exchange-correlation functional or the harmonic approximation is to be blamed for the dissatisfactory agreement with the experimental data.…”

“…In their DFT study of hydrogen chemisorption on neutral copper clusters, Cheng and co-workers have identified Cu 4 to bind dissociated H 2 most strongly and argued that the sharp-corner copper atom allows stronger overlap with their 4 s orbital. 20 , 21 The absolute binding energies cannot be compared due to the fact that we study cationic clusters with a different (more accurate) computational setup including a systematic structure search, but the trend is certainly similar.…”

Effects of Temperature on Enantiomerization Energy and Distribution of Isomers in the Chiral Cu13 Cluster

“…One more Cu atom caps the pentagonal bipyramid; this capping Cu atom is responsible for the chirality of the Cu 13 cluster. Our calculated Cu–Cu bond length on the putative chiral global minimum is 2.432 Å, in good agreement with other reported DFT calculations of a Cu–Cu dimer of 2.248 Å [ 93 ] and also with an experimental bond length of 2.22 [ 94 , 95 ], slightly above 5.3% the experimentally determined value. The calculated vibrational frequency of Cu 13 was 60 cm −1 , whereas the computed vibrational frequency of the Cu–Cu dimer was 245 cm −1 , again in good agreement with the experimental value of 265 cm −1 [ 95 ].…”

Relative Populations and IR Spectra of Cu38 Cluster at Finite Temperature Based on DFT and Statistical Thermodynamics Calculations

“…The optimized Cu-Cu bond length is 2.4670 Å, which is in good agreement with the reported bond length in the Cu-Cu dimer via DFT calculations (2.248 Å) (Kabir et al, 2004;Guvelioglu et al, 2006) and is consistent with the experimental Cu-Cu bonding distance of 2.22 Å (Kabir et al, 2004). Our computed TO structure diameter is 7.8 Å, which is in good agreement with the 8 Å reported in previous DFT calculations (Guvelioglu et al, 2006).…”