OD vibrations and hydration structure in an Al 3 + ( aq ) solutionfrom a Car-Parrinello molecular-dynamics simulation
The optimized geometry, energetics, and vibrational properties of Al ( D 2 O ) n 3 + clusters, with n = 1 , 2 , 4 , and 6, have been studied using plane waves, different local basis sets, different methodologies [density-functional theory, MP2, CCSD(T)], and different functionals (BLYP, PBE). Moreov...
Gespeichert in:
Veröffentlicht in: | The Journal of chemical physics 2006-03, Vol.124 (10), p.104501-104501-13 |
---|---|
Hauptverfasser: | , , |
Format: | Artikel |
Sprache: | |
Online-Zugang: | Volltext |
Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
Zusammenfassung: | The optimized geometry, energetics, and vibrational properties of
Al
(
D
2
O
)
n
3
+
clusters, with
n
=
1
,
2
,
4
, and 6, have been studied using plane waves, different local basis sets, different methodologies [density-functional theory, MP2, CCSD(T)], and different functionals (BLYP, PBE). Moreover, Car-Parrinello molecular-dynamics (MD) simulations using the BLYP functional, plane waves, and the Vanderbilt ultrasoft pseudopotentials have been performed for an aqueous
Al
3
+
solution with 1 ion and 32
D
2
O
molecules in a periodic box at room temperature, studied for
10
ps
. The cluster calculations were performed to pinpoint possible shortcomings of the electronic structure description used in the Car-Parinello MD (CPMD) simulation. For the clusters, the hydration structure and interaction energies calculated with the 'BLYP/plane-wave' approach agree well with high-level
ab initio
methods but the exchange-correlation functional introduces errors in the OD stretching frequencies (both in the absolute values and in the ion-induced shifts). For the aqueous solution, the CPMD simulation yields structural properties in good agreement with experimental data. The CPMD-simulated OD stretching vibrational band for the first-shell water molecules around
Al
3
+
is strongly downshifted by the influence of the ion and is compared with experimental data from the literature. To make such a comparison meaningful, the influences of a number of systematic effects have been addressed, such as the exchange-correlation functional, the fictitious electron mass, anharmonicity effects, and the small box size in the simulation. Each of these factors (except the last one) is found to affect the OD frequency by
100
cm
−
1
or more. The final "corrected" frequencies agree with experiment within
∼
30
cm
−
1
for bulk water but are too little downshifted for the first-shell
Al
3
+
(
aq
)
water molecules (by
∼
200
cm
−
1
). |
---|---|
ISSN: | 0021-9606 1089-7690 |
DOI: | 10.1063/1.2131062 |