@article {541, title = {Selective capture of CO$_{2}$ over N$_{2}$ and CH$_{4}$: B clusters and their size effects}, journal = {Mater. Today Commun.}, volume = {22}, year = {2020}, pages = {100712}, abstract = {Using density-functional theory (DFT), we investigate the selectivity of adsorption of CO$_{2}$ over N$_{2}$ and CH$_{4}$ on planar-type B clusters, based on our previous finding of strong chemisorption of CO$_{2}$ on the B$_{1}$$_{0}$$_{-}$$_{1}$$_{3}$ planar and quasiplanar clusters. We consider the prototype B$_{8}$ and B$_{1}$$_{2}$ planar-type clusters and perform a comparative study of the adsorption of the three molecules on these clusters. We find that, at room temperature, CO$_{2}$ can be separated from N$_{2}$ by selective binding to the B$_{1}$$_{2}$ cluster and not to the B$_{8}$ cluster. Selective adsorption of CO$_{2}$ over CH$_{4}$ at room temperature is possible for both clusters. Based on our DFT-adsorption data (including also a semi-infinite Boron sheet) and the available literature-adsorption value for N$_{2}$ on the planar-type B$_{3}$$_{6}$ cluster, we discuss the selectivity trend of CO$_{2}$ adsorption over N$_{2}$ and CH$_{4}$ with planar-cluster size, showing that it extends over sizes including B$_{1}$$_{0}$$_{-}$$_{1}$$_{3}$ clusters and significantly larger.}, doi = {10.1016/j.mtcomm.2019.100712}, url = {https://www.sciencedirect.com/science/article/abs/pii/S2352492819305719}, author = {Alexandra B. Santos-Putungan and Nata{\v s}a Stoji{\'c} and Nadia Binggeli and Francis N. C. Paraan} } @article {498, title = {Strong chemisorption of CO$_{2}$ on B$_{1}$$_{0}${\textendash}B$_{1}$$_{3}$ planar-type clusters}, journal = {J. Phys. Condens. Matter}, volume = {31}, year = {2019}, pages = {145504}, abstract = {

An ab initio density functional study was performed investigating the adsorption of CO$_{2}$ on neutral boron Bₙ (n = 10{\textendash}13) clusters that are characterized by planar and quasiplanar ground-state atomic structures. For all four clusters, we found large chemisorption binding energies, reaching 1.6 eV between CO$_{2}$ and B$_{1}$$_{2}$, with the adsorbed molecule oriented in the plane of the cluster and adsorbed along the cluster edge. A configuration with chemisorbed dissociated CO$_{2}$ molecule also exists for B$_{1}$$_{1}$ and B$_{1}$$_{3}$ clusters. The strong adsorption is due to the bending of the CO$_{2}$ molecule, which provides energetically accessible fully in-plane frontier molecular orbitals matching the edge states of the clusters. At the same time, the intrinsic dipole moment of a bent CO$_{2}$ molecule facilitates the transfer of excess electronic charge from the cluster edges to the molecule.

}, doi = {10.1088/1361-648x/aafebd}, author = {Alexandra B. Santos-Putungan and Nata{\v s}a Stoji{\'c} and Nadia Binggeli and Francis N. C. Paraan} } @conference {430, title = {Strong chemisorption of CO on neutral B13 cluster edge site}, year = {2017}, month = {8{\textendash}11 Aug 2017}, pages = {PS-03}, publisher = {9th Conference of Asian Consortium on Computational Materials Science}, address = {Kuala Lumpur, Malaysia}, abstract = {We investigate the interaction of carbon monoxide (CO) molecule with neutral boron 13 (B13) cluster using spin-polarized density functional theory (DFT). We found that the edge sites of B13 cluster is the most reactive part, with strong CO adsorption of around -1.67 eV. Molecular orbitals analysis of the cluster shows that~the HOMO nearest to the Fermi level contributes to the adsorption of CO molecule. Our results indicate that~B13 cluster~could have potential applications in the storage and sequestration of CO molecules.}, url = {https://umconference.um.edu.my/accms-9}, author = {Alexandra B. Santos-Putungan and Nata{\v s}a Stoji{\'c} and Nadia Binggeli and Francis N. C. Paraan} } @inproceedings {309, title = {Investigation of neutral B13 clusters: A density functional theory study}, booktitle = {Proceedings of the 34th Samahang Pisika ng Pilipinas Physics Congress}, year = {2016}, month = {18{\textendash}21 Aug 2016}, pages = {SPP-2016-PA-18}, address = {University of the Philippines Visayas, Iloilo City}, abstract = {We investigate the electronic structure of neutral boron_13 (B13) clusters using spin-polarized density functional theory (DFT). The stable B13 cluster is observed to have a two-dimensional planar structure. Energy levels diagram shows that it has a highest occupied molecular orbital{\textendash}lowest unoccupied molecular orbital (HOMO-LUMO) gap of 0.36 eV. Analysis of the electronic charge density of the B13 cluster reveals that most of the electrons are shared between B atoms and are located at the edges, where the HOMO and LUMO are also localized. Our results indicate that the most reactive part of the cluster is along its edges.}, author = {Alexandra B. Santos-Putungan and Nata{\v s}a Stoji{\'c} and Nadia Binggeli and Francis N. C. Paraan} } @conference {santos-putungan-qpcmp-2015, title = {Computational materials science via density functional theory: General introduction and success stories}, year = {2015}, month = {22{\textendash}23 Apr 2015}, publisher = {Workshop on Theories in Quantum Phenomena and Condensed Matter Physics}, address = {University of the Philippines Los Ba{\~n}os, Laguna}, url = {https://imsp.uplb.edu.ph/index.php/component/content/article/17-imsp-news/research/370-workshop-on-theories-in-quantum-phenomena-and-condensed-matter-physics}, author = {Alexandra B. Santos-Putungan} } @inproceedings {santosputungan-spp-2015, title = {Enhanced ferromagnetism in Zn0.5 (Co)0.5 O alloy: DFT calculations}, booktitle = {Proceedings of the 33rd Samahang Pisika ng Pilipinas Physics Congress}, year = {2015}, month = {3{\textendash}6 Jun 2015}, pages = {SPP-2015-PA-14}, address = {University of Northern Philippines, Vigan City}, abstract = {
In this work, we studied the structure and magnetic properties of Zn0.5(Co)0.5O alloy via spin-polarized density functional theory DFT. We utilized a 1 x 1 ZnO hexagonal wurtzite unit cell in a 4-atom bilayer configuration, with one Zn atom replaced by a Co atom. We found that the original lattice parameters of ZnO did not change appreciably upon Co alloying, and thus the structure remains robust. Similarly, minimal charge redistribution between the metals and oxygen is observed. Lastly, our calculations showed that the net magnetization of ZnO upon Co alloying is enhance significantly, much larger than that via doping. The results suggest that\ Zn0.5(Co)0.5O\ as a ferromagnetic material is a potential candidate for advanced spintronic applications.
}, author = {Alexandra B. Santos-Putungan and Joshua Gregor A Dizon and Darwin B Putungan and Francis N. C. Paraan} } @conference {352, title = {Structural and magnetic properties of Zn0.5 Co0.5 O alloy configurations via DFT}, year = {2015}, month = {16{\textendash}18 June 2015}, pages = {56}, publisher = {8th Conference of Asian Consortium on Computational Materials Science}, address = {National Taiwan University of Science and Technology, Taipei}, abstract = {We studied the structure and magnetic properties of ZnCoO alloy configurations via spin-polarized density functional theory (DFT). For the hexagonal wurtzite Zn0.5(Co)0.5O alloy, we used a 1x1x1 ZnO unit cell in a 4-atom bilayer configuration, with one Zn atom replaced by Co. In a similar manner, we utilized a 1x1x1 CoO rocksalt structure, with four Co atoms replaced by Zn to obtain Co0.5(Zn)0.5O. We found that the original ZnO lattice did not change appreciably upon Co alloying, with around 2\% compression, and thus the structure remains robust and atoms bond stronger. This is complemented by Zn0.5(Co)0.5O stronger bulk cohesive energy per formula unit (8.29 eV) compared to bulk ZnO (7.05 eV). Additionally, minimal charge redistribution between the metal atoms and oxygen is observed. On another note, a volume expansion of 3\% was observed for Co0.5(Zn)0.5O, implying the formation of weaker bonds between atoms. The calculated bulk cohesive energy per formula unit for CoO is 9.47 eV, quite larger than that of Co0.5(Zn)0.5O at 8.07 eV. Lastly, our calculations showed that the net magnetization of ZnO upon Co alloying is enhanced significantly, while the reverse is true for Zn-alloyed CoO. The results suggest that Zn0.5(Co)0.5O is more stable in hexagonal wurtzite structure and could be a better controllable ferromagnetic material for spintronics applications.}, url = {http://www.iams.sinica.edu.tw/accms8/program$\#$poster}, author = {Alexandra B. Santos-Putungan and Francis N. C. Paraan} } @inproceedings {salazar-spp-2015, title = {Structural and optical properties of ZnO microrods as fast and efficient UV scintillator materials}, booktitle = {Proceedings of the 33rd Samahang Pisika ng Pilipinas Physics Congress}, year = {2015}, month = {3{\textendash}6 Jun 2015}, pages = {SPP-2015-5B-07}, address = {University of Northern Philippines, Vigan City}, abstract = {
Aqueous chemical grown zinc oxide (ZnO) microrods are found to be crystalline, uniform and well-faceted in terms of structure and morphology. From photoluminescence spectroscopy, these microrods interestingly exhibit ultraviolet (UV) near-band-edge emission at 392 nm (3.16 eV) without any visible or defect-related emission. The UV emission also intensifies with increasing excitation energy. Spectral narrowing is not observed indicating the non-existence of lasing nor stimulated emission from these structures. Having fast luminescence lifetimes less than 100 ps, these ZnO microrods then hold a promise as potential candidates for fast and effcient scintillator materials.
}, author = {Hernanie T Salazar Jr and Alexandra B. Santos-Putungan and Arnel A Salvador and Roland V Sarmago and Melvin John F Empizo and Kohei Yamanoi and Ren Arita and Toshihiko Shimizu and Nobuhiko Sarukura} }