Electronic structure of large modified nickel nanoclusters
A combined method of quantum-chemical semiempirical approach MNDO and molecular dynamics with atomic potentials was used while studying the growth of large nanoclusters of nickel. Geometry and electronic structure of Ni₄₈₅ were studied as well as a series of similar surface (111) substituted (by Pd,...
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Інститут фізики конденсованих систем НАН України
2006
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| Цитувати: | Electronic structure of large modified nickel nanoclusters / V. Pokhmurskii, V. Kopylets, S. Korniy // Condensed Matter Physics. — 2006. — Т. 9, № 4(48). — С. 773–776. — Бібліогр.: 9 назв. — англ. |
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irk-123456789-1214492017-06-15T03:05:55Z Electronic structure of large modified nickel nanoclusters Pokhmurskii, V. Kopylets, V. Korniy, S. A combined method of quantum-chemical semiempirical approach MNDO and molecular dynamics with atomic potentials was used while studying the growth of large nanoclusters of nickel. Geometry and electronic structure of Ni₄₈₅ were studied as well as a series of similar surface (111) substituted (by Pd, Pt, Cu, Mn and Cr) clusters. The role was analysed of the surface electronic density of states (DOS) and their contribution into the processes such as adsorption and surface reaction at catalytic oxidation of carbon monoxide. Stability of all substituted nanoclusters was analyzed and surface electron charges were estimated as negligible in agreement with experiments and exact calculations by periodic ab initio methods. Вивчається процес росту великих нанокластерiв нiкелю iз застосуванням комбiнованого пiдходу на основi квантово-хiмiчного напiвемпiричного MNDO методу та молекулярно-динамiчного методу з атомними потенцiалами. Дослiджується геометрична та електронна структура нанокластера Ni₄₈₅, а також модифiкованих нанокластерiв, утворених при замiщеннi поверхневих атомiв нiкелю атомами паладiю, платини, мiдi, марганцю та хрому. Проаналiзовано роль поверхневих електронних станiв пiд час адсорбцiйних процесiв та поверхневих реакцiй при каталiтичному окисленнi монооксиду вуглецю на поверхнi нанокластерiв нiкелю. Дослiджено стiйкiсть нанокластерiв та розраховано поверхневi електроннi заряди, що узгоджуються з ab initio розрахунками перiодичних структур. 2006 Article Electronic structure of large modified nickel nanoclusters / V. Pokhmurskii, V. Kopylets, S. Korniy // Condensed Matter Physics. — 2006. — Т. 9, № 4(48). — С. 773–776. — Бібліогр.: 9 назв. — англ. 1607-324X PACS: 81.16.Hc, 73.22.-f DOI:10.5488/CMP.9.4.773 http://dspace.nbuv.gov.ua/handle/123456789/121449 en Condensed Matter Physics Інститут фізики конденсованих систем НАН України |
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A combined method of quantum-chemical semiempirical approach MNDO and molecular dynamics with atomic potentials was used while studying the growth of large nanoclusters of nickel. Geometry and electronic structure of Ni₄₈₅ were studied as well as a series of similar surface (111) substituted (by Pd, Pt, Cu, Mn and Cr) clusters. The role was analysed of the surface electronic density of states (DOS) and their contribution into the processes such as adsorption and surface reaction at catalytic oxidation of carbon monoxide. Stability of all substituted nanoclusters was analyzed and surface electron charges were estimated as negligible in agreement with experiments and exact calculations by periodic ab initio methods. |
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Pokhmurskii, V. Kopylets, V. Korniy, S. |
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Pokhmurskii, V. Kopylets, V. Korniy, S. Electronic structure of large modified nickel nanoclusters Condensed Matter Physics |
| author_facet |
Pokhmurskii, V. Kopylets, V. Korniy, S. |
| author_sort |
Pokhmurskii, V. |
| title |
Electronic structure of large modified nickel nanoclusters |
| title_short |
Electronic structure of large modified nickel nanoclusters |
| title_full |
Electronic structure of large modified nickel nanoclusters |
| title_fullStr |
Electronic structure of large modified nickel nanoclusters |
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Electronic structure of large modified nickel nanoclusters |
| title_sort |
electronic structure of large modified nickel nanoclusters |
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Інститут фізики конденсованих систем НАН України |
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2006 |
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http://dspace.nbuv.gov.ua/handle/123456789/121449 |
| citation_txt |
Electronic structure of large modified nickel nanoclusters / V. Pokhmurskii, V. Kopylets, S. Korniy // Condensed Matter Physics. — 2006. — Т. 9, № 4(48). — С. 773–776. — Бібліогр.: 9 назв. — англ. |
| series |
Condensed Matter Physics |
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AT pokhmurskiiv electronicstructureoflargemodifiednickelnanoclusters AT kopyletsv electronicstructureoflargemodifiednickelnanoclusters AT korniys electronicstructureoflargemodifiednickelnanoclusters |
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2025-07-08T19:55:21Z |
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2025-07-08T19:55:21Z |
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1837109895095123968 |
| fulltext |
Condensed Matter Physics 2006, Vol. 9, No 4(48), pp. 773–776
Electronic structure of large modified nickel
nanoclusters
V.Pokhmurskii, V.Kopylets, S.Korniy
Physics and Mechanics Institute of NAS of Ukraine, 5, Naukowa Str., 79601 Lviv, Ukraine
Received January 26, 2006, in final form November 20, 2006
A combined method of quantum-chemical semiempirical approach MNDO and molecular dynamics with
atomic potentials was used while studying the growth of large nanoclusters of nickel. Geometry and electronic
structure of Ni485 were studied as well as a series of similar surface (111) substituted (by Pd, Pt, Cu, Mn and
Cr) clusters. The role was analysed of the surface electronic density of states (DOS) and their contribution
into the processes such as adsorption and surface reaction at catalytic oxidation of carbon monoxide. Stability
of all substituted nanoclusters was analyzed and surface electron charges were estimated as negligible in
agreement with experiments and exact calculations by periodic ab initio methods.
Key words: quantum-chemical and molecular dynamics calculations, nanoclusters, density of states,
catalytic processes, surface
PACS: 81.16.Hc, 73.22.-f
1. Introduction
Both semiempirical and ab initio quantum chemical methods are widely used in the study
of electronic and geometrical structures of large molecules and clusters [1]. However in the case
of ab initio approximations, powerful computers and workstations are required. The situation is
complicated when quantum chemical Hamiltonians are introduced into the statistical molecular
dynamic and Monte Carlo methods. These are needed to obtain a vivid time-dependent picture
of nanocluster development, such as growth and interaction with environment [2]. An attempt
to use standard software (HyperChem [3], etc.) frequently fails due to computational problems.
The information about the change of electron dependent properties would be extremely useful
in preparing the molecules and nanoclusters with new behavior in different fields of physics and
chemistry.
In the present study we managed to use a combined method of semi-empirical quantum chem-
ical and molecular dynamic statistical approximations [4] to calculate equilibrium geometry and
electronic structures by means of personal computer hardware. This simulation makes it possible
to use such an approximation in many researches in a simple and effective manner within short
computer times.
2. Computer model
As it was done previously [4], we used a modified version of the HyperChem 6.0 temporary
and GAMESS [5] software with intrinsic parameters for transition metals [6] by means of the
MNDO method. Large clusters of nickel were constructed on the basis of its elementary f.c.c. cells
to form a final cubo-octahedral structure with large (111) surfaces. The surface atoms of nickel
were subsequently substituted by other atoms (Pt, Pd, Cu, Mn and Cr) to follow the alteration
of the basis cluster electronic properties. The clusters of 13 and 55 atoms were also calculated as
they had structural stability. Large clusters contained up to 500 atoms, the formation of 485 atoms
being stable in a cubo-octahedral structure.
c© V.Pokhmurskii, V.Kopylets, S.Korniy 773
V.Pokhmurskii, V.Kopylets, S.Korniy
3. Results and discussion
In figure 1 we show the tendency of cluster stabilization with the growth of its sizes in all
three directions. At the beginning, the formations are relatively stable only for several atoms
since optimization of geometry is allowed completely. In the middle section a decay of an initial
unoptimized structures is observed (with the exclusion of Ni13 and Ni55). The stability may be
obtained if the number of atoms reaches three hundred and more. Bulk lattice parameter for such
a nickel cluster is 0.315 nm and is in good agreement with the experimental value 0.352 [7]. The
calculated value is natural for such semiempirical method.
Figure 1. Dependence of the calculated parameter of a lattice nickel nanocluster on the number
of atoms.
(a) (b)
(c) (d)
Figure 2. Density of states as a function of energy: a) – surface (111) of Ni485 cluster; b) – volume
of the cluster (second layer and others); c) – surface (111), covered with CO molecules in atop
sites; d) – surface (111) with CO and O2 chemisorbed (CO – atop, O2 – in bridge positions. (c)
and d) are presented with s − p-band as low peaks).
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Electronic structure of large modified nickel nanoclusters
The density of states (DOS) was calculated as a function of energies and the influence of surface
(111), volume and gas chemisorption on DOS was determined for stable structure. Figure 2 shows
the results for pure nickel cluster Ni485.
Part a and b of the figure 2 present the difference in DOS between the surface (111) and volume
(second layer) of the cluster. We see more wide peaks for the latter case. The main peak is also
lower here. We showed the density of states for d-orbitals. If adsorbat is present, the Fermi level is
shifted to the left (more negative values): CO causes the emergence of two main groups of peaks
from s − p-electrons while CO + O2 causes four of them (part c and d).
The results indicate that only the surface is effected and the behavior of the second and the next
layers almost coincides with that of volume. Due to self-consistent calculations, the charge transfer
and values of orbital occupation are easily obtained which enabled us to study the peculiarities of
the surface and the adsorbat.
A perspective view of nickel Ni485 (figure 3) is presented with two adsorption sites – atop and
bridge positions, the latter being shown for similar reaction [9] on the surface (110) of RuO2.
Figure 3. A perspective view of CO and O2 (dissociative) adsorption on the (111) surface of
Ni485 nanocluster on atop (left side) and bridge (upper side) positions.
Next we modified the nickel cluster with noble (Pd and Pt) metal atoms (up to 10%) to change
its electronic properties. The substitution of surface atoms really alters the DOS of nickel cluster
and the shift of energy levels becomes more favorable for surface reaction activation. Thus the
oxidation of carbon monoxide becomes more intensive and the catalytic properties of large nan-
oclusters are improved. However the newly formed structure is slightly unstable (95% as compared
with pure nickel cluster. The implantation of inactive copper atoms (up to 10%) makes the cluster of
worse stability (73%). On the other hand, the substitution of surface nickel atoms with Cr and Mn
presented a nice stability, though the catalytic activity was just a little lost, as compared with pure
Ni485. This may be explained by a decrease in energy level shift in contrast to noble metal effect.
Table 1. Electron excess in the surface (111) for pure nickel cluster and clusters with 10% content
of other transition metals.
Nanocluster Ni485 Ni+Pd Ni+Pt Ni+Cu Ni+Cr Ni+Mn
Electron excess in
the surface (elec-
tron/Ni atom)
0,032 0,035 0,040 0,021 0,026 0,028
The substitution of surface nickel atoms by Cu, Cr and Mn makes the active surface oxidation
possible and serves as an example of d- and s − p-electron effect on the transfer, which causes the
loss of catalytic activity of nickel nanocluster.
775
V.Pokhmurskii, V.Kopylets, S.Korniy
In calculations we observed a negligible excess of electrons in the surface gathered in the table 1.
It may be noticed that noble metals increase the nickel atom charge, and accelerate surface processes
such as chemisorption and surface reactions, 2CO + O2 = 2CO2.
Other transition elements, such as Cr and Mn decrease the electron charge on nickel atoms,
particularly Cu, and they decrease activation of the nanocluster. The change distribution is in
satisfactory agreement with exact periodic ab initio calculations [8].
4. Conclusions
A combined method of quantum chemical semiempirical MNDO approximation and molecular
dynamics made it possible to study the process of large metal nanocluster formation, indicating
some stable structures, Ni13 and Ni55 (known before) and a new Ni485. The substitution of surface
atoms in the cluster by other transition metals causes the change of their geometry stability. The
analysis of electronic structures of the clusters showed the role of density of states, separated into
d- and sp- band, which is important in the surface processes, which determine the catalytic activity
with important practical applications (utilization of harmful gases and liquids, chemical synthesis).
References
1. Stampfl C., Ganduglia-Pirovano M.V., Reuter K., Scheffler M., Surf. Sci., 2002, 500, 368.
2. Valuev A.A., Kaklugin A.S., Norman G.E., Uspechi chimiji, 1995, 64, 643.
3. http://www.hyper.com
4. Pokhmurskii V.I., Kopylets V.I., Korniy S.A., Phys.-Chim. Mech. Mater., 2004, 5, 7.
5. Schmidt M.S., Baldridge K.K., Boatz J.A. et al., J. Comput. Chem., 1993, 14, 1347.
6. Kopylets V.I., Korniy S.A., Phys.-Chim. Mech. Mater., 2002, 2, 120.
7. Roberts M.W., McKee C.S. Chemistry of the metal-gas interface, p. 113–115. Clarendon press, Oxford,
1980.
8. Smith J. Theory of chemisorption, p. 241–327. Springen-Verlag, Berlin, 1980.
9. Reuter K., Frenkel D., Scheffler M., Phys. Rev. Let., 2004, 93, 11, 116105–1.
Електронна структура модифiкованих нанокластерiв нiкелю
В.I.Похмурський, В.I.Копилець, С.А.Корнiй
Фiзико-механiчний iнститут iм. Г.В.Карпенка НАН України, 79061, м. Львiв, вул. Наукова, 5
Отримано 26 сiчня 2006 р., в остаточному виглядi – 20 листопада 2006 р.
Вивчається процес росту великих нанокластерiв нiкелю iз застосуванням комбiнованого пiдходу на
основi квантово-хiмiчного напiвемпiричного MNDO методу та молекулярно-динамiчного методу з
атомними потенцiалами. Дослiджується геометрична та електронна структура нанокластера Ni485,
а також модифiкованих нанокластерiв, утворених при замiщеннi поверхневих атомiв нiкелю атома-
ми паладiю, платини, мiдi, марганцю та хрому. Проаналiзовано роль поверхневих електронних ста-
нiв пiд час адсорбцiйних процесiв та поверхневих реакцiй при каталiтичному окисленнi монооксиду
вуглецю на поверхнi нанокластерiв нiкелю. Дослiджено стiйкiсть нанокластерiв та розраховано по-
верхневi електроннi заряди, що узгоджуються з ab initio розрахунками перiодичних структур.
Ключовi слова: квантово-хiмiчнi та молекулярно-динамiчнi розрахунки, нанокластери, густина
станiв, каталiтичнi процеси, поверхня
PACS: 81.16.Hc, 73.22.-f
776
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