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1.
M. Hartmann R. Mitrić B. Stanca V. Bonačić-Koutecký 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):151-155
Ultrafast ground state nuclear dynamics of Au4 and Ag4 is theoretically explored in the framework of negative ion - to neutral - to positive ion (NeNePo) pump-probe spectroscopy
based on the ab initio Wigner distribution approach. This involves the preparation of a nonequilibrium neutral ensemble by pump induced photodetachment
of a thermal anionic ground state distribution, gradient corrected DFT classical trajectory simulations “on the fly” on the
neutral ground state, and detection of the relaxation process of the ensemble in the cationic ground state by a time-delayed
probe pulse. In Au4, the initially prepared linear structure is close to a local minimum of the neutral state giving rise to characteristic vibrations
in the signals for probe wavelength near the initial Franck-Condon transition. A timescale of ∼1 ps for the structural relaxation towards the stable rhombic D2h neutral isomer was determined by the increase of the signal for probe wavelength in vicinity of the vertical ionization energy
of the rhombic structure. In contrast, the relaxation dynamics in Ag4 is characterized by normal mode vibrations since both the initially prepared anionic ground state and the neutral ground
state have rhombic minimum geometries. Thus, time-resolved oscillations of pump-probe signals are fingerprints of structural
behaviour which can be used experimentally for the identification of particular isomers in the framework of NeNePo spectroscopy.
Received 22 December 2000 相似文献
2.
H. Hogreve 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(1):85-91
Electronic states of the molecular lithium anion are investigated by configuration-interaction calculations. Comparison with
the analogously computed potential energy curves for the lowest singlet and triplet states of the neutral Li2 shows that in addition to the well-known stable ground state X there also exist metastable excited states of Li
2
-
. Within the quartet sector, two candidates for such long-lived states are identified and their spectroscopic properties studied.
Received 23 March 1999 相似文献
3.
R. Mitri C. Bürgel J. Burda V. Bonai-Koutecký P. Fantucci 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):41-44
Bimetallic silver-gold clusters are well suited to study
changes in metallic versus
ionic properties involving charge transfer as a function of
the size and the composition. We present structures, ionization
potentials (IP) and vertical detachment energies (VDE) for
neutral and charged bimetallic
AunAgm (
2(n +
m)5) clusters obtained from
density functional level of theory. In the stable structures of
these clusters Au atoms assume positions which favor charge
transfer from Ag atoms. In clusters with equal numbers of hetero
atoms (n =
m = 1- 4) heteronuclear
bonding is preferred to homonuclear bonding, giving rise to
large values of ionization potentials. For larger clusters
(n=m=5, 10) stable structures do not favor
neither hetero bonding nor segregation into the single
components, although they exhibit more metallic than ionic
features. This remains valid also for
Au8Ag12 cluster
characterized by strong charge transfer to gold subunit. The
influence of doping of pure gold clusters with silver atoms on
VDE and IP values is discussed in context of their reactivity
towards O2 and CO molecules. As a
starting point we consider reactivity towards CO and
O2 molecules on the example of
AgAu- dimer. The results show that
the catalytic cycle can be fullfilled. 相似文献
4.
Optical absorption of isolated silver cluster-tryptophan:
A joint experimental and theoretical study
T. Tabarin R. Antoine I. Compagnon M. Broyer P. Dugourd R. Mitrić J. Petersen V. Bonačić-Koutecký 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):275-278
We present a joint experimental and theoretical gas phase study of photoabsorption and photofragmentation of silver cluster-biomolecule
complexes. We demonstrate on the example of [ Trp.Ag3] + that binding of the metal cluster to a biomolecule leads to a significant enhancement of the photoabsorption in comparison
with [Trp.H]+ and [Trp.Ag]+. This enhancement arises due to the coupling between the excitations in the metallic subunit with charge transfer excitations
between silver cluster and tryptophan. Our experimental studies show that silver clusters up to eleven atoms can be bound
to tryptophan and we present first results on the photofragmentation of the Trp.Ag11
+ complex cation, in which properties of cluster subunit remain preserved. 相似文献
5.
V. Bonačić-Koutecký C. Bürgel L. Kronik A. E. Kuznetsov R. Mitrić 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):471-476
We present structural and optical properties of silver clusters Agn (n=2, 4, 6, 8) at two model support sites of MgO, stoichiometric MgO(100) and FS-center defect, based on density functional theory and embedded cluster model. Our results provide the mechanism responsible
for the absorption and emission patterns due to the specific interaction between the excitations
within the cluster and the support site which is strongly cluster size and structure dependent.
We propose Ag4 at stoichiometric site as well as Ag2, Ag4 and Ag6 at FS-center defects as good candidates for the emissive centers in the visible regime. 相似文献
6.
R. Mitrić U. Werner C. Bürgel V. Bonačić-Koutecký 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):201-204
Here, we present the dynamical aspects and the role of internal energy redistribution
(IVR) in the reactivity of noble metal clusters towards O2. We show on the example of
Ag3O2
- / Ag3O2 / Ag3O2
+ that NeNePo spectroscopy
carried out under zero electron kinetic energy (ZEKE) conditions can be a powerful
tool to investigate the geometry relaxation and IVR induced by photodetachment in real time.
Furthermore, we demonstrate that difference in the reactivity of Ag6
- and Au6
-
towards O2 can be attributed to different nature of the IVR process. Dissipative IVR
in Ag6
- favors fast complex stabilization, whereas resonant IVR found for Au6
- might
be an important factor determining the catalytic activity of Au6
- cluster in the CO oxidation. 相似文献
7.
M. L. Kimble N. A. Moore A. W. Castleman Jr C. Bürgel R. Mitrić V. Bonačić-Koutecký 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):205-208
In this paper,
we present results from our joint experimental and theoretical study of the reactivity
of anionic gold oxide clusters Au2,3O1-4
- towards CO. We provide clear
evidence that, although O–O bond
weakening/dissociation is important to enable CO oxidation,
the presence of atomic oxygen can be favorable but is not always sufficient. Furthermore, we show that with the
addition of a single gold atom the reactivity channels can be changed. As a
consequence, in contrast to CO oxidation in the case of anionic gold dimer oxides,
association of CO or replacement of O2 by CO become
the dominant reaction channels for Au3On
-. This demonstrates the nonscalable
properties of gold clusters in the size regime in which each atom counts. 相似文献
8.
D. R. Justes A. W. Castleman Jr R. Mitri V. Bonai-Koutecký 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):331-334
Density functional calculations have been performed for
the
reactions towards ethylene considering atomic and molecular
oxygen loss, oxygen transfer and association reactions. The
oxygen transfer channel to ethylene is energetically favourable
in contrast to the oxygen loss. This is in agreement with the
experimental results [1] which show that
does not lose atomic oxygen during the collision induced
dissociation at thermal energies. A radical cation mechanism
based on structure-reactivity relation of
cluster is proposed to explain oxygen transfer channel
indicating that this reaction is size selective. 相似文献
9.
Z.F. Liu W.L. Yim J.S. Tse J. Hafner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(1):105-114
Ab initio Molecular Dynamics (MD) method, based on density functional theory (DFT) with planewaves and pseudopotentials, was used to
study the stability and internal motion in silver cluster Agn, with n
=4-6. Calculations on the neutral, cationic and anionic silver dimer Ag2 show that the bond distance and vibrational frequency calculated by DFT are of good quality. Simulations of Ag4, Ag5, and Ag6 in canonical ensemble reveal distinct characteristics and isomerization paths for each cluster. At a temperature of 800 K,
an Ag4 has no definite structure due to internal motion, while for Ag5 and Ag6the clusters maintain the planar structure, with atomic rearrangement observed for Ag5 but not for Ag6. At a temperature of 200 K, Ag4 can exist in two planar structures whilst Ag5 is found to be stable only in the planar form. In contrast Ag6 is stable in both planar trigonal and 3D pentagonal structures. Micro-canonical MD simulation was performed for all three
clusters to obtain the vibrational density of states (DOS).
Received 5 May 1999 and Received in final form 20 August 1999 相似文献
10.
S. F. Chekmarev R. Mitri V. Bonaci-Koutecký 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):45-48
The ab initio molecular
dynamics (AIMD) [1] is combined with the heuristic, successive
confinement method of surveying a potential energy surface (PES)
[2], thereby offering a framework for the simulation study of
kinetics and equilibrium properties of metallic clusters. This
approach is applied to the study of Au4,
a cluster possessing a simple but specific PES, which consists
of very shallow and deep basins and due to this presents a
challenge to the conventional AIMD methods. Among other things,
the probabilities of the transitions between isomers have been
found, and on this basis, both the time-dependent and
equilibrium populations of the isomers have been calculated for
the conditions typical of the NeNePo experiments [3] in the
femtosecond pump-probe spectroscopy. 相似文献
11.
I. Bhattacharyya N. C. Bera A. K. Das 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(2):221-226
Geometrical parameters, harmonic frequencies and molecular properties of FCN, ClCN, their cations and the isomers of FCN and
ClCN are studied in detail using ab initio MP2, CCSD and CCSD(T) methods. The dissociation energy of FCN and ClCN in various
dissociation channels has been
investigated. Both ground and metastable state of the fragmented atoms are considered in their dissociation pathways. The
isomerization energy of FCN and ClCN and the NBO charges of FCN, ClCN, their cations and isomers are analyzed. 相似文献
12.
Y. Yamaguchi J. Gspann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):103-106
Large-scale molecular dynamics simulations with high acceleration energy on a diamond surface were performed in order to investigate
the surface erosion process. Accelerated argon or CO2 clusters (∼960 atoms, 100 keV/cluster) impacted on the (111) surface of diamond which consisted of more than 1,000,000 carbon
atoms. A typical hemispherical crater appeared about 0.7 ps after the impact, and two or three-layered shockwaves were formed
and propagated to certain directions, but the crater was immediately filled up with the fluidized hot carbon material due
to the collective elastic recovery before the reflection of the shockwave. The impact energy of the cluster was at first transferred
mainly as kinetic energy of the diamond surface in a short time, and the potential energy was activated later. The activated
carbon and oxygen atoms from the impact cluster stimulated the evaporation from the diamond surface for the CO2 cluster impact while the evaporation seemed to be suppressed by the argon atoms themselves for the argon cluster impact.
Received 22 November 2000 相似文献
13.
V. Bonačić-Koutecký M. Hartmann J. Pittner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):133-138
We present the ultrafast multistate nuclear dynamics involving adiabatic and nonadiabatic excited states of non-stoichiometric
halide deficient clusters (NanFn-1) characterized by strong ionic bonding and one-excess electron for which the “frozen ionic bonds” approximation has been
justified allowing to consider the optical response of the single excess electron in the effective field of the other electrons.
We combined the Wigner-Moyal representation of the vibronic density matrix with the ab initio multi state molecular dynamics in the ground and excited electronic states including the nonadiabatic couplings calculated
“on the fly” at low computational demand. This method allows the simulation of femtosecond pump-probe and pump-dump signals
based on an analytical formulation, which utilizes temperature dependent ground state initial conditions, an ensemble of trajectories
carried out on the electronic excited state as well as on the ground state after the passage through the conical intersection
in the case of nonadiabatic dynamics and for probing either in the cationic state or in the ground state. The choice of the
systems we presented has been made in order to determine the timescales of the fast geometric relaxation leaving the bonding
frame intact as during the dynamics in the first excited state of Na4F3, and of the bond breaking processes leading to conical intersection between the first excited state and the ground state
as in Na3F2. The former is the smallest finite system prototype for an surface F-center of bulk color centers. The latter allows to study
the photo isomerization in full complexity taking into account all degrees of freedom. In the case of Na4F3 after the fast geometric relaxation in the excited state leading to deformed cuboidal structure without breaking of bonds,
different types of internal vibrational redistribution (IVR) processes have been identified in pump-dump signals by tuning
the dump laser. In contrast, from the analysis of the pump-probe signals of Na3F2 cluster, the timescales for the metallic and the ionic bond breaking, as well as for the passage through conical intersection
have been determined. Finally the conditions under which these processes can be experimentally observed have been identified.
Received 22 December 2000 相似文献
14.
H. Duan F. Ding A. Rosén A. Harutyunyan T. Tokune S. Curtarolo K. Bolton 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):185-189
Molecular dynamics simulations were used to study the
initial growth of single-walled carbon nanotubes (SWNTs) on a supported iron
cluster (Fe50). Statistical analysis shows that the growth direction of
SWNTs becomes more perpendicular to the substrate over time due to the weak
interaction between carbon nanotube and the substrate. The diameter of the
nanotube also increases with the simulation time and approaches the size of
the supported iron cluster. 相似文献
15.
T.A. Beu J. Onoe K. Takeuchi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):205-212
Non-orthogonal tight-binding molecular-dynamics is employed to calculate structural and vibrational properties of C36 and its oligomers (C36)
M = 2, 3, 4
. The lowest energy configuration of the C
36
cage is confirmed to have D
6h
symmetry. For the dimer, too, the D
2h
structure reported in the literature is found. The vibrational spectrum is identified with the power spectrum of the displacement
autocorrelation function. Additional vibrational properties are extracted from the dynamical matrix. For the monomer, fair
agreement with available ab initio calculations is achieved, with comparatively smaller deviations in the Raman-frequencies than for published semi-empirical
calculations. The features of the vibrational modes are correlated with the structural properties of the oligomers.
Received 24 November 2000 and Received in final form 24 August 2001 相似文献
16.
Y. Shimizu S. Sawada K.S. Ikeda 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):365-372
“Spontaneous alloying” observed by Yasuda, Mori et al. for metallic small clusters is simulated using classical Hamiltonian dynamics. Very rapid alloying occurs homogeneously and
cooperatively starting from the solid phase of the cluster if the heat of solution is negative and the size of cluster is
less than a critical size. Analysis of 2D models reveals that the alloying rate obeys an Arrhenius-type law, which predicts
the alloying time much less than second at room temperature. Evidences manifesting that the spontaneous alloying proceeds in the solid phase without melting are
also presented. The simulation reproduces the essential features of the experiments.
Received: 2 March 1998 / Revised: 21 May 1998 / Accepted: 28 May 1998 相似文献
17.
C. Houée-Levin J. Bergès 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):551-555
The mechanisms of protein degradation induced by ionisation are of great interest for radiobiology, improvement of mass spectroscopy
and industrial processes such as radio sterilisation. Sequences containing asparagin are very sensitive especially if surrounded
by glycine. Very few techniques allow a satisfying understanding of the processes induced by creation of an anionic or cationic
site in a peptide. We used the methods of quantum chemistry (DFT/B3LYP with 6-31G* basis set) to characterise the geometry modifications induced in the cations or in the anions derived from peptide Gly Asn
Gly. The cationic sites are localised mostly close to the first peptidic bond and induce a lengthening of the Ca-C(O) bond.
Conversely the anionic sites are localised on a carbonyl function. Implications are discussed considering the radiolytic products
and the proposed mechanisms.
Received 21 January 2002 Published online 13 September 2002 相似文献
18.
R. Parajuli S. Matt O. Echt A. Stamatovic P. Scheier T.D. Märk 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):69-72
We have carried out measurements on metastable fragmentation of mass selected argon cluster ions which are produced by electron
impact ionization of a neutral argon cluster beam. From the shape of the fragment ion peaks (MIKE scan technique) one can
deduce information about the distribution of kinetic energy that is released in the decay reaction. In this study, for Ar
5
+ to Ar
15
+, it is Gaussian and thus we can calculate from the peak width the mean kinetic energy release 〈KER〉 of the corresponding
decay reactions. Using finite heat bath theory we calculate from these data the binding energies of the decaying cluster ions.
Received 20 November 2000 相似文献
19.
Ş. Erkoç H. Kökten Z. Güvenç 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(3):361-365
The fragmentation of water clusters, [(H
2
O)n;n = 2-8], have been investigated by using molecular-dynamics simulation method. In the simulations a polarizable-dissociable
potential energy function for water has been used. Particular attention has bee paid to investigate the effect of structural
properties and cluster size on the fragmentation.
Received 27 April 2000 and Received in final form 6 October 2000 相似文献
20.
G.A. Chass S. Lovas R.F. Murphy I.G. Csizmadia 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):481-497
An exhaustive ab initio and DFT search for energetically stable conformers from the topologically possible set was undertaken on the N-acetyl-phenylalanyl-N-methylamide
and N-acetyl-tyrosyl-N-methylamide systems. The geometries of all 81 phenylalanyl and 162 tyrosyl possible rotamers, described
under the rules outlined by Multi-Dimensional Conformational Analysis (MDCA), were attempted at each of the RHF/3-21G, RHF/6-31G(d)
and B3LYP/6-31G(d) levels of theory. A total of 32 and 66 stable conformational minima were found for the phenylalanyl and
tyrosyl amino acid diamides, respectively, at the B3LYP/6-31G(d) level. From the tyrosyl set, 33 unique conformers emerge
when the orientation of the A
i
3
dihedral angle (p-OH orientation) is disregarded. A total of 31 conformers were common to both sets and showed nearly identical geometries.
The comparison of the optimized DFT geometries of the two systems showed near by perfect linear fits with R2 values of 0.9997, 0.9994, 0.9997, and 0.9996 for the φ
i
, ψ
i
, A
i
1
, and A
i
2
dihedral angles, respectively. Relative energies of the matching 31 conformers also fitted to a linear plot with an R2 value of 0.9985. The geometric centroid of the aromatic ring in the sidechain of both systems was found to be within 4.1
?of the H and O atoms of the peptide groups, in 21 and 2 of the conformers, respectively. None of the non-matching conformers
showed any such interaction distance ≤4.1 ?.
Received 1st February 2002 / Received in final form 28 May 2002 Published online 13 September 2002 相似文献