64 research outputs found
Binding Energies in Benzene Dimers: Nonlocal Density Functional Calculations
The interaction energy and minimum energy structure for different geometries
of the benzene dimer has been calculated using the recently developed nonlocal
correlation energy functional for calculating dispersion interactions. The
comparison of this straightforward and relatively quick density functional
based method with recent calculations can elucidate how the former, quicker
method might be exploited in larger more complicated biological, organic,
aromatic, and even infinite systems such as molecules physisorbed on surfaces,
and van der Waals crystals.Comment: 17 pages, 6 figure
First-principles approach to rotational-vibrational frequencies and infrared intensity for H adsorbed in nanoporous materials
The absorption sites and the low-lying rotational and vibrational (RV) energy
states for H adsorbed within a metal-organic framework are calculated via
van der Waals density functional theory. The induced dipole due to bond
stretching is found to be accurately given by a first-principles driven
approximation using maximally-localized-Wannier-function analysis. The
strengths and positions of lines in the complex spectra of RV transitions are
in reasonable agreement with experiment, and in particular explain the
experimentally mysteriously missing primary line for para hydrogen
Interaction energies of monosubstituted benzene dimers via nonlocal density functional theory
We present density-functional calculations for the interaction energy of
monosubstituted benzene dimers. Our approach utilizes a recently developed
fully nonlocal correlation energy functional, which has been applied to the
pure benzene dimer and several other systems with promising results. The
interaction energy as a function of monomer distance was calculated for four
different substituents in a sandwich and two T-shaped configurations. In
addition, we considered two methods for dealing with exchange, namely using the
revPBE generalized gradient functional as well as full Hartree-Fock. Our
results are compared with other methods, such as Moller-Plesset and
coupled-cluster calculations, thereby establishing the usefulness of our
approach. Since our density-functional based method is considerably faster than
other standard methods, it provides a computational inexpensive alternative,
which is of particular interest for larger systems where standard calculations
are too expensive or infeasible.Comment: submitted to J. Chem. Phy
A Higher-Accuracy van der Waals Density Functional
We propose a second version of the van der Waals density functional (vdW-DF2)
of Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)], employing a more accurate
semilocal exchange functional and the use of a large-N asymptote gradient
correction in determining the vdW kernel. The predicted binding energy,
equilibrium separation, and potential-energy curve shape are close to those of
accurate quantum chemical calculations on 22 duplexes. We anticipate the
enabling of chemically accurate calculations in sparse materials of importance
for condensed-matter, surface, chemical, and biological physics.Comment: 14 pages, 10 figure
Evaluation of New Density Functional with Account of van der Waals Forces by Use of Experimental H2 Physisorption Data on Cu(111)
Detailed experimental data for physisorption potential-energy curves of H2 on
low-indexed faces of Cu challenge theory. Recently, density-functional theory
has been developed to also account for nonlocal correlation effects, including
van der Waals forces. We show that one functional, denoted vdW-DF2, gives a
potential-energy curve promisingly close to the experiment-derived
physisorptionenergy curve. The comparison also gives indications for further
improvements of the functionals
Energetics and dynamics of H adsorbed in a nanoporous material at low temperature
Molecular hydrogen adsorption in a nanoporous metal organic framework
structure (MOF-74) was studied via van der Waals density-functional
calculations. The primary and secondary binding sites for H were confirmed.
The low-lying rotational and translational energy levels were calculated, based
on the orientation and position dependent potential energy surface at the two
binding sites. A consistent picture is obtained between the calculated
rotational-translational transitions for different H loadings and those
measured by inelastic neutron scattering exciting the singlet to triplet (para
to ortho) transition in H. The H binding energy after zero point energy
correction due to the rotational and translational motions is predicted to be
100 meV in good agreement with the experimental value of 90 meV.Comment: 5 pagers, 4 figures. added reference
Analyzing the frequency shift of physiadsorbed CO2 in metal organic framework materials
Combining first-principles density functional theory simulations with IR and
Raman experiments, we determine the frequency shift of vibrational modes of CO2
when physiadsorbed in the iso-structural metal organic framework materials
Mg-MOF74 and Zn-MOF74. Surprisingly, we find that the resulting change in shift
is rather different for these two systems and we elucidate possible reasons. We
explicitly consider three factors responsible for the frequency shift through
physiabsorption, namely (i) the change in the molecule length, (ii) the
asymmetric distortion of the CO molecule, and (iii) the direct influence of
the metal center. The influence of each factor is evaluated separately through
different geometry considerations, providing a fundamental understanding of the
frequency shifts observed experimentally.Comment: 9 pages, 4 figure
Towards a working density-functional theory for polymers: First-principles determination of the polyethylene crystal structure
Equilibrium polyethylene crystal structure, cohesive energy, and elastic
constants are calculated by density-functional theory applied with a recently
proposed density functional (vdW-DF) for general geometries [Phys. Rev. Lett.
92, 246401 (2004)] and with a pseudopotential-planewave scheme. The vdW-DF with
its account for the long-ranged van der Waals interactions gives not only a
stabilized crystal structure but also values of the calculated lattice
parameters and elastic constants in quite good agreement with experimental
data, giving promise for successful application to a wider range of polymers.Comment: 4 pages, 3 figure
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