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Research Activities
General
The research group concentrates on electronic structure calculations in molecular systems
using a large variety of programs and methods. Both imported programs like ACES II/Cfour,
Dalton, Dirac, Gamess, Gaussian, LUCIA, MOLCAS, Molpro, ADF, and Turbomole as well as
locally developed programs are used. The laboratory is also part of the
Finnish Centre of Excellence (2006-2011)
in Computational Molecular Science (CMS)
Search for new chemical species
Recent examples comprise the 'golden fullerenes' WAu12 and Au32,
triple bond to gold in AuC+, five-fold chemical bonds between Ba and a
planar 10π-ring, or the predicted triple U-Ir bond in NUIr, the hydrogen-rich
complexes of type CrH12 or VH12-,
new compounds with new oxidation states such as Hg(IV) or Pu(VIII),
or the carbon dioxide analog CPt2.
Many of these species are already synthesized.
Heavy metals, actinides, and transactinides
The number of electrons at each heavy atom is large and their orbitals
have very different sizes. Relativistic effects, including spin-orbit coupling,
become very important. There are, however, practical ways to meet all these
challenges. Apart from the QED aspect, that should soon be seen for the
valence shell, most of the local activity has become very chemical.
We are intimately connected with most of the leading gold chemists and
some of the actinide chemists, and steadily respond to their needs when they arise.
From the past, the understanding (and naming) of the metallophilic attraction
as a dispersion force, was an important result. There are hundreds of examples
of it, notably in Ag(I), Au(I), or Tl(I) chemistry. A vast area that has
barely been opened is formed by the experimental optical properties of
these compounds. The properties of these systems are the subject for computational
studies at our laboratory.
Computational nanoscience
Nanoscience and nanotechnology are the areas of the fastest development of
materials research and its applications. As in the case of new small molecules,
we are able to perform state-of-the-art computational work in this area.
Our achievements are already substantial particularly in the case of
metal cluster chemistry and in silicon nanoscience.
The optical properties of Si have been found to depend on its structure on
the nanometer scale, and bright photoluminescence from silicon nanoclusters
has been observed. The optical gap of silicon nanocrystals can be 2 - 3 eV
depending on their size, and they can emit light with high efficiency.
The absorption and emission spectra including Franck-Condon shifts of
the silicon clusters have been studied at time-dependent density-functional
theory (TDDFT) and coupled cluster (CC2) levels.
Computational bioscience
Haems, which are important catalysts of biological electron transfer,
are composed of a planar porphyrin structure with iron coordinated at the
centre. It is known from spectroscopy that ferric low-spin heme has
one unpaired electron at the iron, and that this spin is paired as
the heme receives an electron upon reduction. The location of the
surplus electrical charge upon reduction of a heme group has been unclear.
It has been suggested that the charge may be distributed
over the whole heme structure, but electrostatic calculations have also
suggested that the charge is confined to the central iron atom.
This question was unraveled by more rigorous density-functional
and coupled-cluster calculations which showed that the spin pairing
at the iron is accompanied by effective delocalization
of electrons from the iron towards the periphery of the porphyrin ring,
including its substituents. Cell respiration is studied in close
theoretical and experimental collaboration with the Helsinki Bioenergetics
Group.
Magnetically induced molecular currents
Many molecular properties bear the stamp of electron-delocalization
effects and the ability of delocalized electron clouds to sustain
magnetically induced currents. The classical example is molecular
aromaticity which was initially associated with smells or fragrances.
Aromatic molecules were considered to be planar molecules possessing
specific structural characteristics and peculiar chemical reactivities.
The aromaticity concept has more lately been extended to include not
only planar molecular species but also twisted, bent and even
cage-shaped molecules.
However, the extension of the aromaticity concept has not made it
easier to define it unambiguously. The most popular means to classify
molecular aromaticity is related to the strength of the
magnetically induced current circling the molecular rings.
Software development
The following computer programs are being or have recently been developed in our research group:
A configuration-interaction and coupled-cluster program package for
for studies of optical properties such as radiative and non-radiative
recombination rates of electrons and holes confined in semiconductor
quantum dots (QDOT). Collaboration: University of Århus, Åbo Akademi University.
A configuration-interaction program package for ab initio studies
of interacting boson systems (BOSSE). The methods are applied on
Bose-Einstein condensates and helium droplets. Collaboration: Åbo Akademi University.
A program for calculation of magnetically induced currents in molecules using
gauge-including atomic orbitals (GIMIC). Collaboration: University of Mainz, University of Tromsø.
A program employing the direct approach to gravitation and electrostatics (DAGE)
algorithm for fast and accurate computation of electrostatic potentials.Collaboration: University of Tromsø.
A 2-dimensional finite-difference Hartree-Fock program
for diatomic molecules
(2DHF)
Collaboration: Uniwersytet Mikołaja Kopernika, CSC - Scientific Computing Ltd.
Supplementary Publication Information
Supplementary information related to publications by people at our laboratorium can be found
here.
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