List of publications
Note: each reference is a hyperlink pointing, via a DOI, to the corresponding article at the publisher's site. If you would like have the full text (PDF file) of an article of mine that is not already provided below, please ask me.
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Ice and clathrates
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Cage occupancies in nitrogen clathrate hydrates from Monte Carlo simulations
V. Ballenegger
J. Phys. Chem. C
123
16757-16765
(2019)
👁AbstractComparisons of Gibbs ensemble Monte Carlo simulations with experimental data for the cage occupancies in N2 clathrate hydrates are performed to assess the accuracy of such simulations, to refine the effective potentials employed, and to help interpret recently measured large cage over small cage occupancy ratios. Different sets of interaction potentials for N2-N2, N2-H2O and H2O-H2O interactions are considered. Some of them fail to reproduce the known experimental fact that some large cages are doubly occupied at 273 K and high pressures. The best agreement between simulations and experiments is obtained when using a new N-O interaction potential derived in this work by averaging an ab-initio potential energy surface for the N2-H2O dimer.
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Sensitivity of predicted gas hydrate occupancies on treatment of intermolecular interactions
C. Thomas, S. Picaud, V. Ballenegger, and O. Mousis
J. Chem. Phys.
132
104510
(2010)
👁AbstractThe sensitivity of gas hydrate occupancies predicted on the basis
of van der Waals-Platteeuw theory is investigated, as a function
of the intermolecular guest-water interaction potential model, and
of the number of water molecules taken into account. Simple analytical
correction terms that account for the interactions with the water
molecules beyond the cutoff distance are introduced, and shown to
improve significantly the convergence rate, and hence the efficiency
of the computation of the Langmuir constants. The predicted cage
occupancies in pure methane and pure carbon dioxide clathrates, calculated
using different recent guest-water pair potentials models derived
from ab initio calculations, can vary significantly depending on
the model. That sensitivity becomes especially strong in the case
of multiple guest clathrates. It is shown that the abundances of
coenclathrated molecules in multiple guest clathrate hydrates potentially
formed on the surface of Mars can vary by more than two orders of
magnitude depending on the model. These results underline the strong
need for experimental data on pure and multiple guest clathrate hydrates,
in particular in the temperature and pressure range that are relevant
in extreme environment conditions, to discriminate among the theoretical
models.
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Variability of the methane trapping in martian subsurface clathrate hydrates
C. Thomas, O. Mousis, S. Picaud, and V. Ballenegger
Planet. Space Sci.
57
42--47
(2009)
👁AbstractRecent observations have evidenced traces of methane (CH(4)) heterogeneously
distributed in the martian atmosphere. However, because the lifetime
of CH(4) in the atmosphere of Mars is estimated to be around 300-600
years on the basis of photochemistry, its release from a subsurface
reservoir or an active primary source of methane have been invoked
in the recent literature. Among the existing scenarios, it has been
proposed that clathrate hydrates located in the near subsurface of
Mars could be at the origin of the small quantities of the detected
CH(4). Here, we accurately determine the composition of these clathrate
hydrates, as a function of temperature and gas phase composition,
by using a hybrid statistical thermodynamic model based on experimental
data. Compared to the other recent works, our model allows us to
calculate the composition of clathrate hydrates formed from a more
plausible composition of the martian atmosphere by considering its
main compounds, i.e. carbon dioxide, nitrogen and argon, together
with methane. Besides, because there is no low temperature restriction
in our model, we are able to determine the composition of clathrate
hydrates formed at temperatures corresponding to the extreme ones
measured in the polar caps. Our results show that methane enriched
clathrate hydrates could be stable in the subsurface of Mars only
if a primitive CH(4)-rich atmosphere has existed or if a subsurface
source of CH(4) has been (or is still) present.
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Clathration of volatiles in the solar nebula and implications for the origin of titan's atmosphere
O. Mousis, J. I. Lunine, C. Thomas, M. Pasek, U. Marbaeuf, Y. Alibert, V. Ballenegger, D. Cordier, Y. Ellinger, F. Pauzat, and S. Picaud
Astrophys. J.
691
1780--1786
(2009)
👁AbstractWe describe a scenario of Titan's formation matching the constraints
imposed by its current atmospheric composition. Assuming that the
abundances of all elements, including oxygen, are solar in the outer
nebula, we show that the icy planetesimals were agglomerated in the
feeding zone of Saturn from a mixture of clathrates with multiple
guest species, so-called stochiometric hydrates such as ammonia hydrate,
and pure condensates. We also use a statistical thermodynamic approach
to constrain the composition of multiple guest clathrates formed
in the solar nebula. We then infer that krypton and xenon, that are
expected to condense in the 20-30 K temperature range in the solar
nebula, are trapped in clathrates at higher temperatures than 50
K. Once formed, these ices either were accreted by Saturn or remained
embedded in its surrounding subnebula until they found their way
into the regular satellites growing around Saturn. In order to explain
the carbon monoxide and primordial argon deficiencies of Titan's
atmosphere, we suggest that the satellite was formed from icy planetesimals
initially produced in the solar nebula and that were partially devolatilized
at a temperature not exceeding similar to 50 K during their migration
within Saturn's subnebula. The observed deficiencies of Titan's atmosphere
in krypton and xenon could result from other processes that may have
occurred both prior to or after the completion of Titan. Thus, krypton
and xenon may have been sequestrated in the form of XH(3)(+) complexes
in the solar nebula gas phase, causing the formation of noble gas-poor
planetesimals ultimately accreted by Titan. Alternatively, krypton
and xenon may have also been trapped efficiently in clathrates located
on the satellite's surface or in its atmospheric haze. We finally
discuss the subsequent observations that would allow us to determine
which of these processes is the most likely.
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A theoretical investigation into the trapping of noble gases by clathrates on Titan
C. Thomas, S. Picaud, O. Mousis, and V. Ballenegger
Planet. Space Sci.
56
1607--1617
(2008)
👁AbstractIn this paper, we use a statistical thermodynamic approach to quantify
the efficiency with which clathrates on the surface of Titan trap
noble gases. We consider different values of the Ar, Kr, Xe, CH(4),
C(2)H(6) and N(2) abundances in the gas phase that may be representative
of Titan's early atmosphere. We discuss the effect of the various
parameters that are chosen to represent the interactions between
the guest species and the ice cage in our calculations. We also discuss
the results of varying the size of the clathrate cages. We show that
the trapping efficiency of clathrates is high enough to significantly
decrease the atmospheric concentrations of Xe and, to a lesser extent,
of Kr, irrespective of the initial gas phase composition, provided
that these clathrates are abundant enough on the surface of Titan.
In contrast, we find that Ar is poorly trapped in clathrates and,
as a consequence, that the atmospheric abundance of argon should
remain almost constant. We conclude that the mechanism of trapping
noble gases via clathration can explain the deficiency in primordial
Xe and Kr observed in Titan's atmosphere by Huygens, but that this
mechanism is not sufficient to explain the deficiency in Ar.
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Clathrate hydrates as a sink of noble gases in Titan's atmosphere
C. Thomas, O. Mousis, V. Ballenegger, and S. Picaud
Astron. Astrophys.
474
L17--L20
(2007)
👁AbstractWe use a statistical thermodynamic approach to determine the composition
of clathrate hydrates which may form from a multiple compound gas
whose composition is similar to that of Titan's atmosphere. Assuming
that noble gases are initially present in this gas phase, we calculate
the ratios of xenon, krypton and argon to species trapped in clathrate
hydrates. We find that these ratios calculated for xenon and krypton
are several orders of magnitude higher than in the coexisting gas
at temperature and pressure conditions close to those of Titan's
present atmosphere at ground level. Furthermore we show that, by
contrast, argon is poorly trapped in these ices. This trapping mechanism
implies that the gas-phase is progressively depleted in xenon and
krypton when the coexisting clathrate hydrates form whereas the initial
abundance of argon remains almost constant. Our results are thus
compatible with the deficiency of Titan's atmosphere in xenon and
krypton measured by the Huygens probe during its descent on January
14, 2005. However, in order to interpret the subsolar abundance of
primordial Ar also revealed by Huygens, other processes that occurred
either during the formation of Titan or during its evolution must
be also invoked.
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Molecular dynamics study of diffusion of formaldehyde in ice
V. Ballenegger, S. Picaud, and C. Toubin
Chem. Phys. Lett.
432
78--83
(2006)
👁AbstractWe report a Molecular Dynamics simulation study of the diffusion process
of formaldehyde (CH2O) in proton-disordered ice Ih at atmospheric
pressure, in the temperature range 200-273 K. CH2O molecules diffuse
in ice predominantly by jumping between B sites (bond-breaking mechanism),
but substitutional diffusion can also be observed. At 260 K, the
diffusion constant is predicted to be 4 x 10(-7) cm(2)/S with the
TIP4P-Ew water model, and 3 x 10(-7) cm(2)/S with the TIP4P/Ice water
model.
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Particle-Mesh Ewald and P3M methods
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Communication: On the origin of the surface term in the Ewald formula
V. Ballenegger
J. Chem. Phys.
140
161102
(2014)
👁Abstract{A transparent derivation of the Ewald formula for the electrostatic
energy of a periodic three-dimensional system of point charges is
presented. The problem of the conditional convergence of the lattice sum
is dealt with by separating off, in a physically natural and
mathematically simple way, long-range non-absolutely integrable
contributions in the series. The general expression, for any summation
order, of the surface (or dipole) term emerges very directly from those
long-range contributions. (C) 2014 AIP Publishing LLC.}
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How to Convert SPME to P3M: Influence Functions and Error Estimates
V. Ballenegger, J. J. Cerda, and C. Holm
J. Chem. Theory Comput.
8
936--947
(2012)
👁AbstractWe demonstrate explicitly how the two seemingly different particle
mesh Ewald methods, the smooth particle mesh Ewald (SPME) and the
particle particle particle mesh (P3M), can be mathematically transformed
into each other. This allows us in particular to convert the error
estimate of the P3M method in the energy-conserving scheme (also
known as "P3M with analytic differentiation") into an error estimate
for the SPME method, via a simple change of the lattice Green function.
Our error estimate is valid for any values of the SPME parameters
(mesh size, spline interpolation order, Ewald splitting parameter,
real-space cutoff distance), including odd orders of splines. The
problem with the self-forces is avoided thanks to an analytical formula
that allows to subtract them directly within the particle mesh calculation.
Plots of the accuracy of the SPME forces are provided for a wide
range of parameter values. The main use of the error estimate is
to allow simulation program to scan quickly the multidimensional
parameter space to find the best set of parameters to achieve a target
accuracy at the smallest computational cost. As a byproduct, we show
how a SPME code can be transformed into a P3M version by changing
a few lines of code. We demonstrate also that the P3M lattice Green
function can be approximated by a closed farm expression, computable
on-the-fly, that provides essentially the same accuracy as the full
function.
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Removal of spurious self-interactions in particle-mesh methods
V. Ballenegger, J. J. Cerda, and C. Holm
Comput. Phys. Commun.
182
1919--1923
(2011)
👁AbstractWe derive an analytic formula for subtracting the spurious self-forces
in particle-mesh methods that use the analytical differentiation
scheme, such as the Smooth Particle Mesh Ewald (SPME) method and
the Particle-Particle Particle-Mesh (P3M) method with analytical
differentiation. The impact of the self-forces on the accuracy of
the particle-mesh methods is investigated, and it is shown that subtracting
them can improve the accuracy of the calculation for some choices
of the method's parameters. It is also suggested to subtract exactly
the approximate, mesh-computed, self-energy of each particle, replacing
them by the exact value. Subtracting in this way the self-energy
and self-force of each particle not only improves the accuracy, but
also reduces the violation of momentum and energy conservation in
particle-mesh methods with analytical differentiation.
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Particle-particle particle-mesh method for dipolar interactions: On error estimates and efficiency of schemes with analytical differentiation and mesh interlacing
J. J. Cerda, V. Ballenegger, and C. Holm
J. Chem. Phys.
135
184110
(2011)
👁AbstractThe interlaced and non-interlaced versions of the dipolar particle-particle
particle-mesh (P(3)M) method implemented using the analytic differentiation
scheme (AD-P(3)M) are presented together with their respective error
estimates for the calculation of the forces, torques, and energies.
Expressions for the optimized lattice Green functions, and for the
Madelung self-forces, self-torques and self-energies are given. The
applicability of the theoretical error estimates are thoroughly tested
and confirmed in several numerical examples. Our results show that
the accuracy of the calculations can be improved substantially when
the approximate (mesh computed) Madelung self-interactions are subtracted.
Furthermore, we show that the interlaced dipolar AD-P(3)M method
delivers a significantly higher accuracy (which corresponds approximately
to using a twice finer mesh) than the conventional method, allowing
thereby to reduce the mesh size with respect to the non-interlaced
version for a given accuracy. In addition, we present similar expressions
for the dipolar ik-differentiation interlaced scheme, and we perform
a comparison with the AD interlaced scheme. Rough tests for the relative
speed of the dipolar P(3)M method using ik-differentiation and the
interlaced/non-interlaced AD schemes show that when FFT computing
time is the bottleneck, usually when working at high precisions,
the interlaced AD-scheme can be several times faster than the other
two schemes. For calculations with a low accuracy requirement, the
interlaced version can perform worse than the ik and the non-interlaced
AD schemes.
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Simulations of non-neutral slab systems with long-range electrostatic interactions in two-dimensional periodic boundary conditions
V. Ballenegger, A. Arnold, and J. J. Cerda
J. Chem. Phys.
131
094107
(2009)
👁AbstractWe introduce a regularization procedure to define electrostatic energies
and forces in a slab system of thickness h that is periodic in two
dimensions and carries a net charge. The regularization corresponds
to a neutralization of the system by two charged walls and can be
viewed as the extension to the two-dimensional (2D)+h geometry of
the neutralization by a homogeneous background in the standard three-dimensional
Ewald method. The energies and forces can be computed efficiently
by using advanced methods for systems with 2D periodicity, such as
MMM2D or P3M/ELC, or by introducing a simple background-charge correction
to the Yeh-Berkowitz approach of slab systems. The results are checked
against direct lattice sum calculations on simple systems. We show,
in particular, that the Madelung energy of a 2D square charge lattice
in a uniform compensating background is correctly reproduced to high
accuracy. A molecular dynamics simulation of a sodium ion close to
an air/water interface is performed to demonstrate that the method
does indeed provide consistent long-range electrostatics. The mean
force on the ion reduces at large distances to the image-charge interaction
predicted by macroscopic electrostatics. This result is used to determine
precisely the position of the macroscopic dielectric interface with
respect to the true molecular surface.
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The optimal P3M algorithm for computing electrostatic energies in periodic systems
V. Ballenegger, J. J. Cerda, O. Lenz, and C. Holm
J. Chem. Phys.
128
034109
(2008)
👁AbstractWe optimize Hockney and Eastwood's particle-particle particle-mesh
algorithm to achieve maximal accuracy in the electrostatic energies
(instead of forces) in three-dimensional periodic charged systems.
To this end we construct an optimal influence function that minimizes
the root-mean-square (rms) errors of the energies. As a by-product
we derive a new real-space cutoff correction term, give a transparent
derivation of the systematic errors in terms of Madelung energies,
and provide an accurate analytical estimate for the rms error of
the energies. This error estimate is a useful indicator of the accuracy
of the computed energies and allows an easy and precise determination
of the optimal values of the various parameters in the algorithm
(Ewald splitting parameter, mesh size, and charge assignment order).
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P3M algorithm for dipolar interactions
J. J. Cerda, V. Ballenegger, O. Lenz, and C. Holm
J. Chem. Phys.
129
234104
(2008)
👁AbstractAn extension to the (PM)-M-3 algorithm for electrostatic interactions
is presented that allows to efficiently compute dipolar interactions
in periodic boundary conditions. Theoretical estimates for the root-mean-square
error of the forces, torques, and the energy are derived. The applicability
of the estimates is tested and confirmed in several numerical examples.
A comparison of the computational performance of the new algorithm
to a standard dipolar-Ewald summation methods shows a performance
crossover from the Ewald method to the dipolar (PM)-M-3 method for
as few as 300 dipolar particles. In larger systems, the new algorithm
represents a substantial improvement in performance with respect
to the dipolar standard Ewald method. Finally, a test comparing point-dipole-based
and charged-pair based models shows that point-dipole-based models
exhibit a better performance than charged-pair based models.
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