arXiv subjects

Sajeev S. Chacko

Publications and source records attributed to Sajeev S. Chacko.

2 recordsLinked to original sources

arXiv2026

Structural, Energetic, Electronic, and Vibrational Properties of Boron-Substituted Tungsten Clusters

We report a study of the density functional theory of the structural, electronic and vibrational properties of small tungsten-boron clusters using the B3LYP exchange-correlation functional together with the QZVP basis set. A large number of possible isomeric structures were generated using the USPEX code interfaced with Gaussian 03, and the lowest-energy configurations were selected for detailed analysis. The results show that the addition of boron significantly modifies the geometry of tungsten clusters by reducing their symmetry and leading to the formation of shorter and stronger W-B and B-B bonds. With increasing boron concentration, boron atoms preferentially occupy edge and outer positions and gradually form interconnected B-B links within the clusters. These structural modifications improve the overall stability of the clusters, as reflected by the increase in binding energy, HOMO-LUMO energy gap, ionization potential, and chemical hardness with increasing boron concentration. The eigenvalue spectra show a greater separation between the occupied and unoccupied electronic states after boron substitution, indicating enhanced electronic stabilization and stronger electron localization. Vibrational analysis further reveals a gradual shift from low-frequency W-W vibrational modes in pure tungsten clusters to higher-frequency W-B and B-B stretching modes in boron-rich clusters, indicating an increase in the covalent character of bonding. Overall, the results show that boron improves the stability of tungsten clusters by modifying their bonding and electronic properties at the atomic scale

cond-mat.mtrl-sci↗

arXiv2024

Structural and Energetic Stability of the Lowest Equilibrium Structures of Water Clusters

In the present work, the low-lying structures of 20 different-sized water clusters are extensively searched using the artificial bee colony algorithm with TIP4P classical force field. To obtain the lowest equilibrium geometries, we select the 10 lowest configurations for further minimization using density functional theory. The resulting structures are lower in energy than previously reported results. The structural and energetic stability of these clusters are studied using various descriptors such as binding energy, ionization potentials, fragmentation energy, first and second energy difference, vibrational and optical spectra. The energetic analysis shows that clusters with N = 4, 8, 12, 14, 16 and 19 are more stable. The analysis of fragmentation energies also supports these findings. Our calculations show that non-covalent interactions play a significant role in stabilizing the water clusters. The infrared spectra of water clusters display three distinct bands: intermolecular O...H vibrations, 23 to 1191 cm^-1, intramolecular H-O-H bending, 1600 to 1741 cm^-1, and O-H stretching, 3229 to 3877 cm^-1. The strongest intensity is observed in the low-frequency symmetric stretching modes, along with a noticeable red shift in the stretching vibrations. The optical band gap ranges from 7.14 eV to 8.17 eV and lies in the ultraviolet region. The absorption spectra also show line broadening for clusters with n>=10, resulting in an increase in spectral lines. Interestingly, only the stable clusters exhibit maximum oscillator strength, with the first excitation in all cases corresponding to a π-to-σ* transition.

physics.atm-clus↗