Theoretical Investigation On The Structures And Properties Of Pd₂Si_n And Hf_n Clusters As Well As L-ascorbic Acid And Their Derivatives

The geometrical,electronic properties and Growth Patterns of the bimetal Pd₂doped Si_n(n=10-20) clusters and Hf_n(n=2-13,14,18) as well as the antioxidantactivity of L-Ascorbic acid and their derivatives are studied by using densityfunctional methods. The main research results are as follows:The geometrical and electronic properties and growth patterns of the bimetal Pd₂doped Si_n(n=10-20) clusters are successively investigated. The growth-patternbehaviors, relative stabilities, charge-transfer, and chemical bonding of these clustersare discussed. The optimized geometries exhibit that the dominant growth patterns ofPd₂Si_n(n=10-20) are based on pentagonal prism Pd₂Si10and the bimetal Pd₂are dopedopened cagelike silicon clusters at n=10-15 while the Pd₂are completely encapsulatedinside Si_nframes at n=16-20. The encapsulated Pd₂in the Si_nframes are varied underthe interactions of the Pd₂and Si_nframes which are examined in term of thecalculated Pd-Pd distance. The calculated fragmentation energies reveal that theremarkable stable Pd₂Si_nclusters with n=11, 13, 16, 18, and 20 are observed and thePd₂-doped Si16cluster is the most stable species in all different sized clusters.Particularly, Pd₂Si₁₆geometry is obviously distinct as compared to Mo2Si16and thecritical size of geometry transition is n=16. Natural population analysis manifests thatthe charge-transfer phenomena appearing in the Pd₂-doped Si_nclusters are analogousto those of the Mo2doped silicon clusters. In addition, the properties of frontierorbitals of Pd₂-doped Si_n(n=10-20) clusters show that the Pd₂Si_n(n=10, 13, 14, 16,and 17) isomers have enhanced chemical stabilities because of their largerHOMO-LUMO gaps.The geometries, electronic and magnetic properties of Hf_n(n=2-13,14,18)clusters are calculated. Particularly, the studies focus on the averaged atomic bindingenergies, equilibrium geometries, detachment energies, and magnetic characteristicsof Hf_nclusters. Relative stabilities of Hf_nclusters in terms of the calculateddetachment energies are discussed, exhibiting that the magic numbers of stabilities aren=4, 7, 9, and 12, and that the nonmagnetic Hf12geometry is the most stable isomerand ground state. Furthermore, the calculated HOMO-LUMO gap of Hf_n(n=6-13)displays a small odd-even oscillation feature. The calculated ground state magneticmoments for Hf_nare respective 4.0μ B(n=4,11), 2.0μ B(n=2,3,5,7-9,13), and 0.0μB (n=3,6,10,12,14,18); the averaged atomic magnetic moment of Hfnis generallydecreased as the number of n being increased. Comparison our calculated results withavailable experimental data are made.The geometries, stabilities, and antioxidant activity of L-Ascorbic acid (1a),D-Erythroascorbate (2a), and D-erythroascorbate glucoside (3a) as well as their sulfurand selenium derivatives (1b, 1c, 2b, 2c, 3b, and 3c) are presented. Emphasis is placedon studies that focus on the two main running mechanisms, i.e., hydrogen atomdonation and single-electron transfer, and the bond dissociation enthalpy (BDE) forthe O-H bonds and the ionization potential (IP) were computed in the gas phase and inwater solution. Results indicated that the importance of the 2-OH group in thefive-membered ring as donate a H atom to the free radicals, inactivating them. Inwater solution, the antioxidant capacity and the electron donating ability are increased(1c>1b>1a, 2c>2b>2a, 3c>3b>3a) when the O atom in the five-membered ring for 1a,2a, and 3a is replaced by S and Se, respectively. Compared with the standardantioxidant (resveratrol), reflecting these nine compounds has the lower BDE and thehigher IP.