J/A+A/690/A34 Vanadium oxide clusters in substellar atmos. (Lecoq-Molinos+ 2024)
Vanadium oxide clusters in substellar atmospheres. A quantum chemical study.
Lecoq-Molinos H., Gobrecht D., Sindel J.P., Helling C., Decin L.
<Astron. Astrophys. 690, A34 (2024)>
=2024A&A...690A..34L 2024A&A...690A..34L (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics
Keywords: astrochemistry - molecular data - planets and satellites: atmospheres
Abstract:
As a refractory material vanadia (solid V2O5) is likely to be found as
a condensate in the atmospheres of substellar objects such as
exoplanets and brown dwarfs. However, the nature of the
nanometer-sized vanadium oxide clusters that partake in the nucleation
process is not well understood.
We aim to understand the formation of cloud condensation nuclei in
oxygen-rich substellar atmospheres by calculating fundamental
properties of the energetically most favorable vanadium oxide
molecules and clusters and to investigate how they contribute to the
formation of condensation seeds.
We applied a hierarchical optimization approach in order to find the
most favorable structures for clusters of (VO)N and (VO2)N for N=1-10,
and of (V2O5)N for N=1-4 and to calculate their thermodynamical
potentials. The candidate geometries are initially optimized by
applying classical interatomic potentials; these are then refined at
the B3LYP/cc-pVTZ level of theory to obtain accurate zeropoint
energies and thermochemical quantities.
We present previously unreported vanadium oxide cluster structures as
the lowest-energy isomers. Moreover, we report revised cluster
energies and their thermochemical properties. Chemical equilibrium
calculations are used to asses the impact of the updated and newly
derived thermodynamic potentials on the gas-phase abundances of
vanadium-bearing species. In chemical equilibrium, larger clusters
from different stoichiometric families are found to be the most
abundant vanadium-bearing species for temperatures below ∼1000K, while
molecular VO is the most abundant between ∼1000K and ∼2000K. We
determine the nucleation rates of each stoichiometric family for a
given (Tgas, pgas) profile of a brown dwarf using both classical and
non-classical nucleation theory.
Small differences in the revised Gibbs free energies of the clusters
have a large impact on the abundances of vanadium-bearing species in
chemical equilibrium at temperatures below ∼1000K. These abundance
changes subsequently have an impact on the nucleation rates of each
stoichiometric family. We find that with the revised and more accurate
cluster data non- classical nucleation rates are up to 15 orders of
magnitude higher than classical nucleation rates.
Description:
VO: There are 20 data entries in this archive corresponding to the
coordinates and thermochemical data of each (VO)N molecular cluster of
size N=1-10.
VO2: There are 20 data entries in this archive corresponding to the
coordinates and thermochemical data of each (VO2)N molecular clusters
of size N=1-10.
V205: There are 8 data entries in this archive corresponding to the
coordinates and thermochemical data of each (V2O5)N molecular cluster
of size N = 1-4.
The first entries (cN_x.dat) are the final cluster coordinates
obtained after an optimization with the GAUSSIAN16 software at the
B3LYP/cc-pVTZ level of theory. We provide the coordinates for the
lowest energy isomer (global minima candidate) found for each cluster
size. Each file contains the cartesian coordinates (x,y,z) of the
atoms in the clusters, and is labelled cN_x.dat, with N representing
the cluster size and x the energetic ranking (1 for all of the
clusters presented).
The next entries (tN_x.dat) correspond to the thermochemical data of
each cluster, for which we have performed a frequency calculation of
the optimized clusters applying the RRHO approximation. The files are
labelled tN_x.dat, where N is again the cluster size and x the
energetic ranking. The thermochemical table for each cluster includes:
a temperature tange (T), the entropy (S), difference to reference
enthalpy (H-Ho), free enthalpy of formation ({DELTA}H) and Gibbs
free energy of formation ({DELTA}G).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
vo/c1_1.dat 36 2 Coordinates of the global minima candidate
for the V1O1 cluster
vo/c2_1.dat 31 4 Coordinates of the global minima candidate
for the V2O2 cluster
vo/c3_1.dat 36 6 Coordinates of the global minima candidate
for the V3O3 cluster
vo/c4_1.dat 36 8 Coordinates of the global minima candidate
for the V4O4 cluster
vo/c5_1.dat 36 10 Coordinates of the global minima candidate
for the V5O5 cluster
vo/c6_1.dat 36 12 Coordinates of the global minima candidate
for the V6O6 cluster
vo/c7_1.dat 36 14 Coordinates of the global minima candidate
for the V7O7 cluster
vo/c8_1.dat 36 16 Coordinates of the global minima candidate
for the V8O8 cluster
vo/c9_1.dat 36 18 Coordinates of the global minima candidate
for the V9O9 cluster
vo/c10_1.dat 36 20 Coordinates of the global minima candidate
for the V10O10 cluster
vo/t1_1.dat 102 61 Thermochemical data for the global minima
candidate for the V1O1 cluster
vo/t2_1.dat 102 61 Thermochemical data for the global minima
candidate for the V2O2 cluster
vo/t3_1.dat 102 61 Thermochemical data for the global minima
candidate for the V3O3 cluster
vo/t4_1.dat 101 61 Thermochemical data for the global minima
candidate for the V4O4 cluster
vo/t5_1.dat 102 61 Thermochemical data for the global minima
candidate for the V5O5 cluster
vo/t6_1.dat 102 61 Thermochemical data for the global minima
candidate for the V6O6 cluster
vo/t7_1.dat 101 61 Thermochemical data for the global minima
candidate for the V7O7 cluster
vo/t8_1.dat 102 61 Thermochemical data for the global minima
candidate for the V8O8 cluster
vo/t9_1.dat 100 61 Thermochemical data for the global minima
candidate for the V9O9 cluster
vo/t10_1.dat 101 61 Thermochemical data for the global minima
candidate for the V10O10 cluster
vo2/c1_1.dat 36 3 Coordinates of the global minima candidate
for the VO2 cluster
vo2/c2_1.dat 36 6 Coordinates of the global minima candidate
for the V2O4 cluster
vo2/c3_1.dat 36 9 Coordinates of the global minima candidate
for the V3O6 cluster
vo2/c4_1.dat 36 12 Coordinates of the global minima candidate
for the V4O8 cluster
vo2/c5_1.dat 36 15 Coordinates of the global minima candidate
for the V5O10 cluster
vo2/c6_1.dat 36 18 Coordinates of the global minima candidate
for the V6O12 cluster
vo2/c7_1.dat 36 21 Coordinates of the global minima candidate
for the V7O14 cluster
vo2/c8_1.dat 36 24 Coordinates of the global minima candidate
for the V8O16 cluster
vo2/c9_1.dat 36 27 Coordinates of the global minima candidate
for the V9O18 cluster
vo2/c10_1.dat 36 30 Coordinates of the global minima candidate
for the V10O20 cluster
vo2/t1_1.dat 101 61 Thermochemical data for the global minima
candidate for the VO2 cluster
vo2/t2_1.dat 101 61 Thermochemical data for the global minima
candidate for the V2O4 cluster
vo2/t3_1.dat 101 61 Thermochemical data for the global minima
candidate for the V3O6 cluster
vo2/t4_1.dat 100 61 Thermochemical data for the global minima
candidate for the V4O8 cluster
vo2/t5_1.dat 100 61 Thermochemical data for the global minima
candidate for the V5O10 cluster
vo2/t6_1.dat 100 61 Thermochemical data for the global minima
candidate for the V6O12 cluster
vo2/t7_1.dat 100 61 Thermochemical data for the global minima
candidate for the V7O14 cluster
vo2/t8_1.dat 100 61 Thermochemical data for the global minima
candidate for the V8O16 cluster
vo2/t9_1.dat 101 61 Thermochemical data for the global minima
candidate for the V9O18 cluster
vo2/t10_1.dat 100 61 Thermochemical data for the global minima
candidate for the V10O20 cluster
v2o5/c1_1.dat 36 7 Coordinates of the global minima candidate
for the V2O5 cluster
v2o5/c2_1.dat 36 14 Coordinates of the global minima candidate
for the V4O10 cluster
v2o5/c3_1.dat 36 21 Coordinates of the global minima candidate
for the V6O15 cluster
v2o5/c4_1.dat 36 28 Coordinates of the global minima candidate
for the V8O20 cluster
v2o5/t1_1.dat 101 61 Thermochemical data for the global minima
candidate for the V2O5 cluster
v2o5/t2_1.dat 100 61 Thermochemical data for the global minima
candidate for the V4O10 cluster
v2o5/t3_1.dat 100 61 Thermochemical data for the global minima
candidate for the V6O15 cluster
v2o5/t4_1.dat 100 61 Thermochemical data for the global minima
candidate for the V8O20 cluster
--------------------------------------------------------------------------------
Byte-by-byte Description of file: v*/c*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Tab Table identifier, NN_N
6 A1 --- Atom Atomic symbol of the atom
8- 16 F9.6 0.1nm x x coordinate of the atom [Angstrom]
18- 26 F9.6 0.1nm y y coordinate of the atom [Angstrom]
28- 36 F9.6 0.1nm z z coordinate of the atom [Angstrom]
--------------------------------------------------------------------------------
Byte-by-byte Description of file: v*/t*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Tab Table identifier, NN_N
8- 14 F7.2 K T Temperature
16- 34 F19.14 J/mol/K S Entropy S
35- 57 F23.17 kJ/mol H-Ho Enthalpy difference to reference temperature
(298.15)
59- 80 F22.16 kJ/mol DELTAfH Enthalpy of formation
81-102 F22.16 kJ/mol DELTAfG Gibbs free energy of formation
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Acknowledgements:
Helena Lecoq Molinos, helena.lecoq(at)oeaw.ac.at
(End) Patricia Vannier [CDS] 15-Jul-2024