Jesus Ugalde | Euskal Herriko Unibersitatea (original) (raw)
Papers by Jesus Ugalde
![Research paper thumbnail of Correction: The stability of biradicaloid versus closed-shell [E(μ-XR)]2 (E = P, As; X = N, P, As) rings. Does aromaticity play a role?](https://attachments.academia-assets.com/120144536/thumbnails/1.jpg)
](Physical Chemistry Chemical Physics, 2018
![Research paper thumbnail of Methane activation by alternant [N2O2]+ and [N2S2]+ cluster radical cations](https://attachments.academia-assets.com/120144535/thumbnails/1.jpg)
](International Journal of Mass Spectrometry, Apr 1, 2019
Methane activation reaction by small alternant [N 2 Y 2 ] • + (Y O, S) radical cation rings is pr... more Methane activation reaction by small alternant [N 2 Y 2 ] • + (Y O, S) radical cation rings is predicted by the methods of computational chemistry. Approximate density functional theory and coupled cluster singles and doubles with perturbative triples calculations are employed to investigate the potential energy surface of this putative reaction. On the contrary to previously reported methane activation processes by square planar four-membered rings following the proton coupled electron transfer mechanism, the [N 2 O 2 ] • + and [N 2 S 2 ] • + clusters, according to our results, may activate methane through the hydrogen atom transfer mechanism. On the contrary, the similar oxide cluster in which the nitrogen atoms were substituted by phosphorous atoms, [P 2 O 2 ] • + , does not perform methane activation.
Canadian Journal of Chemistry, Dec 1, 2016
The non-monotonic bahavior of the electron repulsion energy and the interelectronic distance, as ... more The non-monotonic bahavior of the electron repulsion energy and the interelectronic distance, as a function of the internuclear separation, in the 3 Πu excited state of the hydrogen molecule has been assessed by explicitly calculation and analysis of the electron-pair density distribution functions from high level ab initio Full Configuration Interaction wave functions, for both the 3 Πu and the 1 Πu states. Additionally, the Hund's rule as applied to these two states has been accounted for in terms of simple electronic shielding effects induced by wave function antisymmetrization.
Journal of Chemical Physics, Aug 21, 2007
The second excited 1 ⌺ g + state of the hydrogen molecule, the so-called GK state, has a potentia... more The second excited 1 ⌺ g + state of the hydrogen molecule, the so-called GK state, has a potential energy curve with double minima. At the united atom limit it converges to the 1s3d configuration of He. At large internuclear distances R, it dissociates to two separated atoms, one in the ground state and another in the 2p excited state. Radial pair density calculations and natural orbital analyses reveal unusual effect of electron correlation around the K minimum of the potential energy curve. As R Ͼ 2.0 a.u., a natural orbital of u symmetry joins the two natural orbitals of g symmetry at smaller R. The average interelectronic distance decreases as the internuclear distance increases from R = 2.0 to 3.0 a.u. Around R = 3.0 a.u. the singly peaked pair density curve splits into two peaks. The inner peak can be attributed to the formation of the ionic electron configuration ͑1s͒ 2 , where both 1s electrons are on the same nucleus. As the two 1s electrons run into different nuclei, one of the two 1s electrons is promoted to the 2p state, which results in the outer peak in the pair density curve. The Rydberg 1s2p configuration persists as the nuclei stretch, and becomes dominant at large R where four natural orbitals, two of g and two of u symmetry, become responsible.
ChemPhysChem, Jan 20, 2022
Using Fourier-transform ion cyclotron resonance mass spectrometry, it was experimentally determin... more Using Fourier-transform ion cyclotron resonance mass spectrometry, it was experimentally determined that Sc + in the highly diluted gas phase reacts with SO 2 to form ScO + and SO. By 18 O labeling, ScO + was shown to play the role of a catalyst when further reacting with SO 2 in a Mars-van Krevelen-like oxygen exchange process. High-level quantum chemical calculations confirmed that the multi-step process to form ScO + and SO is exoergic and kinetically favored. The reaction starts from the triplet surface and although three spin-crossing points with minimal energy have been identified by computational means, there is no evidence that a two-state scenario is involved in the course of the reaction, by which the reactants could switch from the triplet to the singlet surface and back. Pivotal to the oxygen exchange reaction of ScO + with SO 2 is the occurrence of a highly symmetric four-membered cyclic intermediate by which two oxygen atoms become equivalent.
The Journal of Physical Chemistry, 1996
Journal of Physical Chemistry A, Feb 12, 2018
The chemical formation process from the study of radial intracule densities by constructing the r... more The chemical formation process from the study of radial intracule densities by constructing the relaxation holes, ∆h(u), resulting from the difference between the actual radial intracule density and the nonrelaxed one, which is obtained from atomic radial intracule densities and the pair density constructed from the overlap of the atomic densities has been studied. Our results show that the internal reorganization of electron pairs prior to bond formation and the covalent bond formation from electrons in separate atoms are completely recognizable processes from the shape of the relaxation hole, ∆h(u). The magnitude of ∆h(u), the shape of ∆h(u) ∀u < R eq and the distance between the minimum and the maximum in ∆h(u) provide further information about the nature of the chemical bond formed. A computational affordable approach to calculate the radial intracule density from approximate pair densities has been also suggested, paving the way to study electronpair distributions in larger systems.
Journal of Physical Chemistry A, Oct 2, 2017
Journal of Chemical Physics, Aug 14, 2016
We report a joint photoelectron spectroscopy and theoretical study on AuC 4 − , AuC 6 − , and AuC... more We report a joint photoelectron spectroscopy and theoretical study on AuC 4 − , AuC 6 − , and AuC n H − (n = 2, 4, and 6) using high-resolution photoelectron imaging and ab initio calculations. The ground state of AuC 2 H − , AuC 4 H − , and AuC 6 H − is found to be linear, while that of AuC 4 − and AuC 6 − is bent. All the species are found to be linear in their neutral ground states. The electron affinities (EAs) are measured to be 3.366(1) and 3.593(1) eV for AuC 4 and AuC 6 , respectively. Both bending and stretching frequencies are resolved in the spectra of AuC 4 − and AuC 6 −. High-resolution data of AuC n H − reveal major vibrational progressions in the Au-C stretching and bending modes. AuC 2 H − has a ground state stretching frequency of 445(10) cm −1 and a bending frequency of 260(10) cm −1 ; AuC 4 H − has a ground state stretching frequency of 340(10) cm −1 ; AuC 6 H − has a ground state stretching frequency of 260(10) cm −1 and a bending frequency of 55(10) cm −1. The EAs are measured to be 1.475(1), 1.778(1), and 1.962(1) eV for AuC 2 H, AuC 4 H, and AuC 6 H, respectively. The strength of the Au-C bond decreases as the number of carbon atoms increases. The current study provides a wealth of electronic structure information about AuC 4 − , AuC 6 − , and AuC n H − (n = 2, 4, and 6) and their corresponding neutrals.
Canadian Journal of Chemistry, Oct 1, 1996
The dissociation energy of the Ti(OH2)+ ion–molecule complex was calculated by the multiconfigura... more The dissociation energy of the Ti(OH2)+ ion–molecule complex was calculated by the multiconfigurational self-consistent field theory, coupled cluster theory, and two density functional theory based methods, using both all-electron basis sets and effective core potentials. The calculations show that approximate density functional theory gives results in better agreement with experiment than either the multiconfigurational self-consistent field theory or the coupled cluster theory, with both all-electron basis sets and effective core potentials. Nevertheless, the optimized geometries and harmonic vibration frequencies are very similar, irrespective of the level of theory used. The interconfigurational energy ordering of the two valence electronic configurations dn−1s and dn−2s2 of the 4F electronic state of the titanium cation were also calculated and are discussed. Key words: ab initio, dissociation energy, ion–molecule complex, effective core potentials, transition metals.
Journal of Physical Chemistry C, Jun 2, 2016
Recently, plasmonic resonances in molecules, clusters, and nanostructures have gathered a lot of ... more Recently, plasmonic resonances in molecules, clusters, and nanostructures have gathered a lot of attention for their potential range of applicability. Unlike other metal nanostructures, a wide variety of aluminum nanostructures show very promising plasmonic properties. Theoretical and computational investigations helped to understand the nature of collective excitations in such finite systems. However, such theoretical investigations are based on qualitative approaches rather than accurate quantitative methods. In the present work, the collectivity of the low-lying states of Al13– are investigated within the time-dependent density functional theory and analyzed through different computational tools. A novel tool, which provides a quantitative index of the collective nature of the electronic excitations, has been introduced, the so-called transition inverse participation ratio (TIPR) index. The obtained results suggest the presence of plasmonic-like transitions in the Al13– cluster and that these transitio...
ChemInform, Mar 15, 2005
Structure C 1000 Clusters of II-VI Materials: Cd i X i , X: S, Se, Te, i ≤ 16.-The structures of ... more Structure C 1000 Clusters of II-VI Materials: Cd i X i , X: S, Se, Te, i ≤ 16.-The structures of the title clusters are characterized using the hybrid B3LYP DFT method. Clusters with i ≤ 5 exhibit ringlike structures, whereas clusters with i = 6-16 show three-dimensional spheroid structures which are built up from Cd2X2 squares and Cd3X3 hexagons. Second-order free energy differences reveal that the most stable spheroids are the i = 12 ones.-(MATXAIN*,
Physical Chemistry Chemical Physics, 2016
High-level multiconfigurational self-consistent field calculations, supplemented with multiconfig... more High-level multiconfigurational self-consistent field calculations, supplemented with multiconfigurational quasi-degenerate perturbation theory ab initio calculations with the aug-cc-pVTZ basis set, demonstrate that the [E(μ-XH)]2 (E = P, As; X = N, P, As) compounds possess one planar and one butterfly-like isomer. The calculations predict that for X = N, planar isomers, which bear substantial biradicaloid character, are more stable than their butterfly-like counterpart isomers, which feature closed-shell electronic structures. This has been ascribed to the fact that the increased bond angle strain at E-N-E is not compensated by the E-E σ (deformed) bond formation in the butterfly-like isomers, yielding the planar structures, which hold wider E-N-E bond angles, as the most stable isomers. As N is substituted by heavier atoms, either P or As, the E-P(As)-E bond angle strain is released and, additionally, as the formed E-E σ-bond is less deformed, the butterfly isomer becomes the most stable isomer. Subsequent evaluation of the normalized Giambiagi multicenter electron delocalization indices revealed no sign of electron delocalization in the four-membered rings and consequently, it is concluded that aromaticity does not play any role in the stabilization of the planar isomers.
Journal of Physical Chemistry A, Jul 1, 1997
ABSTRACT
Nano Letters, Nov 10, 2020
An enantiopure, conductive, and paramagnetic crystalline 3-D metal−organic framework (MOF), based... more An enantiopure, conductive, and paramagnetic crystalline 3-D metal−organic framework (MOF), based on Dy(III) and the L-tartrate chiral ligand, is proved to behave as an almost ideal electron spin filtering material at room temperature, transmitting one spin component only, leading to a spin polarization (SP) power close to 100% in the ±2 V range, which is conserved over a long spatial range, larger than 1 μm in some cases. This impressive spin polarization capacity of this class of nanostructured materials is measured by means of magnetically polarized conductive atomic force microscopy and is attributed to the Chirality-Induced Spin Selectivity (CISS) effect of the material arising from a multidimensional helicity pattern, the inherited chirality of the organic motive, and the enhancing influence of Dy(III) ions on the CISS effect, with large spin−orbit coupling values. Our results represent the first example of a MOF-based and CISS-effect-mediated spin filtering material that shows a nearly perfect SP. These striking results obtained with our robust and easy-to-synthesize chiral MOFs constitute an important step forward in to improve the performance of spin filtering materials for spintronic device fabrication.
Physical Review Letters, Nov 24, 1997
Journal of Physical Chemistry A, Aug 1, 1998
We have performed an ab initio study of aluminum(III) cation with the aspartic and glutamic amino... more We have performed an ab initio study of aluminum(III) cation with the aspartic and glutamic amino acid residues, i.e., the carboxylate group. Density functional theory methodology was used, and the covalent and noncovalent interactions were analyzed using natural bond orbital theory. First we have investigated the smallest functional moiety of these amino acids, the carboxylate anion. Additionally, we have sequentially introduced two methyl groups to more accurately represent the aspartic and glutamic acid chains. We have compared these data with the nontoxic metal cation, e.g., magnesium(II). Our calculations demonstrate that aluminum(III) binds much more tightly to the ligands than magnesium(II) and the addition of the methyl groups leads to stronger bonds, though the effect of the second methyl group is less than that of the first.
Physical Review A, Oct 2, 2001
The improvements in the characterization of II-VI-compound-based solar cells and the recent exper... more The improvements in the characterization of II-VI-compound-based solar cells and the recent experimental characterization of small clusters and nanoparticles make the study of small II-VI clusters very interesting. In this work, the ground states of small Zn i X i clusters are studied, XϭSe,Te, iϭ1-9. Ringlike structures have been found to be the global minima for clusters as large as iϭ5, and three-dimensional spheroid structures for larger ones, iϭ6Ϫ9. This trend has been ascribed to the stability of obtuse X-Zn-X angles in the first case, and to the stability gained from higher coordination in the second case. The three-dimensional structures may be envisioned as being built from Zn 2 X 2 and Zn 3 X 3 rings, as it was the case for Zn i S i and Zn i O i threedimensional structures. Calculated natural charges are larger as cluster size increases, showing a tendency towards bulk charges.
Physical Chemistry Chemical Physics, 2018
International Journal of Mass Spectrometry, Apr 1, 2019
Methane activation reaction by small alternant [N 2 Y 2 ] • + (Y O, S) radical cation rings is pr... more Methane activation reaction by small alternant [N 2 Y 2 ] • + (Y O, S) radical cation rings is predicted by the methods of computational chemistry. Approximate density functional theory and coupled cluster singles and doubles with perturbative triples calculations are employed to investigate the potential energy surface of this putative reaction. On the contrary to previously reported methane activation processes by square planar four-membered rings following the proton coupled electron transfer mechanism, the [N 2 O 2 ] • + and [N 2 S 2 ] • + clusters, according to our results, may activate methane through the hydrogen atom transfer mechanism. On the contrary, the similar oxide cluster in which the nitrogen atoms were substituted by phosphorous atoms, [P 2 O 2 ] • + , does not perform methane activation.
Canadian Journal of Chemistry, Dec 1, 2016
The non-monotonic bahavior of the electron repulsion energy and the interelectronic distance, as ... more The non-monotonic bahavior of the electron repulsion energy and the interelectronic distance, as a function of the internuclear separation, in the 3 Πu excited state of the hydrogen molecule has been assessed by explicitly calculation and analysis of the electron-pair density distribution functions from high level ab initio Full Configuration Interaction wave functions, for both the 3 Πu and the 1 Πu states. Additionally, the Hund's rule as applied to these two states has been accounted for in terms of simple electronic shielding effects induced by wave function antisymmetrization.
Journal of Chemical Physics, Aug 21, 2007
The second excited 1 ⌺ g + state of the hydrogen molecule, the so-called GK state, has a potentia... more The second excited 1 ⌺ g + state of the hydrogen molecule, the so-called GK state, has a potential energy curve with double minima. At the united atom limit it converges to the 1s3d configuration of He. At large internuclear distances R, it dissociates to two separated atoms, one in the ground state and another in the 2p excited state. Radial pair density calculations and natural orbital analyses reveal unusual effect of electron correlation around the K minimum of the potential energy curve. As R Ͼ 2.0 a.u., a natural orbital of u symmetry joins the two natural orbitals of g symmetry at smaller R. The average interelectronic distance decreases as the internuclear distance increases from R = 2.0 to 3.0 a.u. Around R = 3.0 a.u. the singly peaked pair density curve splits into two peaks. The inner peak can be attributed to the formation of the ionic electron configuration ͑1s͒ 2 , where both 1s electrons are on the same nucleus. As the two 1s electrons run into different nuclei, one of the two 1s electrons is promoted to the 2p state, which results in the outer peak in the pair density curve. The Rydberg 1s2p configuration persists as the nuclei stretch, and becomes dominant at large R where four natural orbitals, two of g and two of u symmetry, become responsible.
ChemPhysChem, Jan 20, 2022
Using Fourier-transform ion cyclotron resonance mass spectrometry, it was experimentally determin... more Using Fourier-transform ion cyclotron resonance mass spectrometry, it was experimentally determined that Sc + in the highly diluted gas phase reacts with SO 2 to form ScO + and SO. By 18 O labeling, ScO + was shown to play the role of a catalyst when further reacting with SO 2 in a Mars-van Krevelen-like oxygen exchange process. High-level quantum chemical calculations confirmed that the multi-step process to form ScO + and SO is exoergic and kinetically favored. The reaction starts from the triplet surface and although three spin-crossing points with minimal energy have been identified by computational means, there is no evidence that a two-state scenario is involved in the course of the reaction, by which the reactants could switch from the triplet to the singlet surface and back. Pivotal to the oxygen exchange reaction of ScO + with SO 2 is the occurrence of a highly symmetric four-membered cyclic intermediate by which two oxygen atoms become equivalent.
The Journal of Physical Chemistry, 1996
Journal of Physical Chemistry A, Feb 12, 2018
The chemical formation process from the study of radial intracule densities by constructing the r... more The chemical formation process from the study of radial intracule densities by constructing the relaxation holes, ∆h(u), resulting from the difference between the actual radial intracule density and the nonrelaxed one, which is obtained from atomic radial intracule densities and the pair density constructed from the overlap of the atomic densities has been studied. Our results show that the internal reorganization of electron pairs prior to bond formation and the covalent bond formation from electrons in separate atoms are completely recognizable processes from the shape of the relaxation hole, ∆h(u). The magnitude of ∆h(u), the shape of ∆h(u) ∀u < R eq and the distance between the minimum and the maximum in ∆h(u) provide further information about the nature of the chemical bond formed. A computational affordable approach to calculate the radial intracule density from approximate pair densities has been also suggested, paving the way to study electronpair distributions in larger systems.
Journal of Physical Chemistry A, Oct 2, 2017
Journal of Chemical Physics, Aug 14, 2016
We report a joint photoelectron spectroscopy and theoretical study on AuC 4 − , AuC 6 − , and AuC... more We report a joint photoelectron spectroscopy and theoretical study on AuC 4 − , AuC 6 − , and AuC n H − (n = 2, 4, and 6) using high-resolution photoelectron imaging and ab initio calculations. The ground state of AuC 2 H − , AuC 4 H − , and AuC 6 H − is found to be linear, while that of AuC 4 − and AuC 6 − is bent. All the species are found to be linear in their neutral ground states. The electron affinities (EAs) are measured to be 3.366(1) and 3.593(1) eV for AuC 4 and AuC 6 , respectively. Both bending and stretching frequencies are resolved in the spectra of AuC 4 − and AuC 6 −. High-resolution data of AuC n H − reveal major vibrational progressions in the Au-C stretching and bending modes. AuC 2 H − has a ground state stretching frequency of 445(10) cm −1 and a bending frequency of 260(10) cm −1 ; AuC 4 H − has a ground state stretching frequency of 340(10) cm −1 ; AuC 6 H − has a ground state stretching frequency of 260(10) cm −1 and a bending frequency of 55(10) cm −1. The EAs are measured to be 1.475(1), 1.778(1), and 1.962(1) eV for AuC 2 H, AuC 4 H, and AuC 6 H, respectively. The strength of the Au-C bond decreases as the number of carbon atoms increases. The current study provides a wealth of electronic structure information about AuC 4 − , AuC 6 − , and AuC n H − (n = 2, 4, and 6) and their corresponding neutrals.
Canadian Journal of Chemistry, Oct 1, 1996
The dissociation energy of the Ti(OH2)+ ion–molecule complex was calculated by the multiconfigura... more The dissociation energy of the Ti(OH2)+ ion–molecule complex was calculated by the multiconfigurational self-consistent field theory, coupled cluster theory, and two density functional theory based methods, using both all-electron basis sets and effective core potentials. The calculations show that approximate density functional theory gives results in better agreement with experiment than either the multiconfigurational self-consistent field theory or the coupled cluster theory, with both all-electron basis sets and effective core potentials. Nevertheless, the optimized geometries and harmonic vibration frequencies are very similar, irrespective of the level of theory used. The interconfigurational energy ordering of the two valence electronic configurations dn−1s and dn−2s2 of the 4F electronic state of the titanium cation were also calculated and are discussed. Key words: ab initio, dissociation energy, ion–molecule complex, effective core potentials, transition metals.
Journal of Physical Chemistry C, Jun 2, 2016
Recently, plasmonic resonances in molecules, clusters, and nanostructures have gathered a lot of ... more Recently, plasmonic resonances in molecules, clusters, and nanostructures have gathered a lot of attention for their potential range of applicability. Unlike other metal nanostructures, a wide variety of aluminum nanostructures show very promising plasmonic properties. Theoretical and computational investigations helped to understand the nature of collective excitations in such finite systems. However, such theoretical investigations are based on qualitative approaches rather than accurate quantitative methods. In the present work, the collectivity of the low-lying states of Al13– are investigated within the time-dependent density functional theory and analyzed through different computational tools. A novel tool, which provides a quantitative index of the collective nature of the electronic excitations, has been introduced, the so-called transition inverse participation ratio (TIPR) index. The obtained results suggest the presence of plasmonic-like transitions in the Al13– cluster and that these transitio...
ChemInform, Mar 15, 2005
Structure C 1000 Clusters of II-VI Materials: Cd i X i , X: S, Se, Te, i ≤ 16.-The structures of ... more Structure C 1000 Clusters of II-VI Materials: Cd i X i , X: S, Se, Te, i ≤ 16.-The structures of the title clusters are characterized using the hybrid B3LYP DFT method. Clusters with i ≤ 5 exhibit ringlike structures, whereas clusters with i = 6-16 show three-dimensional spheroid structures which are built up from Cd2X2 squares and Cd3X3 hexagons. Second-order free energy differences reveal that the most stable spheroids are the i = 12 ones.-(MATXAIN*,
Physical Chemistry Chemical Physics, 2016
High-level multiconfigurational self-consistent field calculations, supplemented with multiconfig... more High-level multiconfigurational self-consistent field calculations, supplemented with multiconfigurational quasi-degenerate perturbation theory ab initio calculations with the aug-cc-pVTZ basis set, demonstrate that the [E(μ-XH)]2 (E = P, As; X = N, P, As) compounds possess one planar and one butterfly-like isomer. The calculations predict that for X = N, planar isomers, which bear substantial biradicaloid character, are more stable than their butterfly-like counterpart isomers, which feature closed-shell electronic structures. This has been ascribed to the fact that the increased bond angle strain at E-N-E is not compensated by the E-E σ (deformed) bond formation in the butterfly-like isomers, yielding the planar structures, which hold wider E-N-E bond angles, as the most stable isomers. As N is substituted by heavier atoms, either P or As, the E-P(As)-E bond angle strain is released and, additionally, as the formed E-E σ-bond is less deformed, the butterfly isomer becomes the most stable isomer. Subsequent evaluation of the normalized Giambiagi multicenter electron delocalization indices revealed no sign of electron delocalization in the four-membered rings and consequently, it is concluded that aromaticity does not play any role in the stabilization of the planar isomers.
Journal of Physical Chemistry A, Jul 1, 1997
ABSTRACT
Nano Letters, Nov 10, 2020
An enantiopure, conductive, and paramagnetic crystalline 3-D metal−organic framework (MOF), based... more An enantiopure, conductive, and paramagnetic crystalline 3-D metal−organic framework (MOF), based on Dy(III) and the L-tartrate chiral ligand, is proved to behave as an almost ideal electron spin filtering material at room temperature, transmitting one spin component only, leading to a spin polarization (SP) power close to 100% in the ±2 V range, which is conserved over a long spatial range, larger than 1 μm in some cases. This impressive spin polarization capacity of this class of nanostructured materials is measured by means of magnetically polarized conductive atomic force microscopy and is attributed to the Chirality-Induced Spin Selectivity (CISS) effect of the material arising from a multidimensional helicity pattern, the inherited chirality of the organic motive, and the enhancing influence of Dy(III) ions on the CISS effect, with large spin−orbit coupling values. Our results represent the first example of a MOF-based and CISS-effect-mediated spin filtering material that shows a nearly perfect SP. These striking results obtained with our robust and easy-to-synthesize chiral MOFs constitute an important step forward in to improve the performance of spin filtering materials for spintronic device fabrication.
Physical Review Letters, Nov 24, 1997
Journal of Physical Chemistry A, Aug 1, 1998
We have performed an ab initio study of aluminum(III) cation with the aspartic and glutamic amino... more We have performed an ab initio study of aluminum(III) cation with the aspartic and glutamic amino acid residues, i.e., the carboxylate group. Density functional theory methodology was used, and the covalent and noncovalent interactions were analyzed using natural bond orbital theory. First we have investigated the smallest functional moiety of these amino acids, the carboxylate anion. Additionally, we have sequentially introduced two methyl groups to more accurately represent the aspartic and glutamic acid chains. We have compared these data with the nontoxic metal cation, e.g., magnesium(II). Our calculations demonstrate that aluminum(III) binds much more tightly to the ligands than magnesium(II) and the addition of the methyl groups leads to stronger bonds, though the effect of the second methyl group is less than that of the first.
Physical Review A, Oct 2, 2001
The improvements in the characterization of II-VI-compound-based solar cells and the recent exper... more The improvements in the characterization of II-VI-compound-based solar cells and the recent experimental characterization of small clusters and nanoparticles make the study of small II-VI clusters very interesting. In this work, the ground states of small Zn i X i clusters are studied, XϭSe,Te, iϭ1-9. Ringlike structures have been found to be the global minima for clusters as large as iϭ5, and three-dimensional spheroid structures for larger ones, iϭ6Ϫ9. This trend has been ascribed to the stability of obtuse X-Zn-X angles in the first case, and to the stability gained from higher coordination in the second case. The three-dimensional structures may be envisioned as being built from Zn 2 X 2 and Zn 3 X 3 rings, as it was the case for Zn i S i and Zn i O i threedimensional structures. Calculated natural charges are larger as cluster size increases, showing a tendency towards bulk charges.