Funding

1
Excess Electrons in Water Clusters, Interfaces,
and the Bulk
Laszlo Turi Adam Madarasz (Eotvos Loring U.,
Budapest) Wen-Shyan Sheu (Fu-Jen University,
Taipei) Daniel Borgis (Universite dEvry / ENS
Paris)

• Funding
• National Science Foundation
• R. A. Welch Foundation
• Hungarian Science Foundation
• Eötvös Fellowship
• Bolyai János Fellowship
• Széchenyi Professor Fellowship

2
Water Cluster Anions distinct isomers

• Systematic variations
• What are the characteristic properties which
  distinguish the different classes?
• Common sets of structural motifs?
• Backing pressure/thermodynamic conditions.
  Non-equilibrium?

3
Anionic clusters and hydrated electronslocalizat
ion mode/binding motif and structure
?
clusters
infinite cluster
?
4
The Toolkit for Mixed Quantum-Classical MD
Simulations
quantum mechanical e- classical solvent
molecules

• Components
• N classical water molecules (SPC model internal
  flexibility)
• the excess electron (wave function represented on
  dual k,r grid)
• the electron-molecule interaction
  (pseudopotential)
• the force acting on the molecular nuclei
• classical force (from the solvent) quantum
  force (from the solute)
• FH2O FQ
• A sampling scheme (adiabatic) time evolution of
  the system

Turi, L. Gaigeot, M.-P. Levy, N. Borgis,
D. J. Chem. Phys., 2001, 114, 7805. Turi,
L. Borgis, D. J. Chem. Phys., 2002, 117, 6186.
5
Applicability of the Pseudopotential
E0 -3.12 eV ? Es-p,max 1.92 eV (vs.
1.72) RG ltr2gt1/2 2.4 A ?

• Bulk
• VDE for n12 clusters
• MP2/6-31(13)G
• vs.
• the pseudopotential

Turi, L. Madarász, Á. Rossky, P. J. JCP 125,
014308 (2006).
6
Cluster Simulations Surface states vs. internal
states
n 20, 30, 45, 66, 104, 200 500, 1000 nominal
T 100K, 200K, 300K
(s ? p n 45. T 200K)
L. Turi, W.-S. Sheu, P. J. Rossky, Science 309,
914 (2005), ibid. 310, 1719 (2005).
7
Average surface state energetic behavior vs.
interior states and vs. expt.
old lines, new points n 200, 500,
1000 (surface and internal at 200K)
expt. (M. Johnson coworkers)
- spectral gap
(expt)
internal
(expt)
E0
internal
0
0.1
0.3
0.2
n -1/3
8
Electron radius and kinetic energy
9
Hydrated electrons at water/vacuum
interfacesthe infinite cluster limit

• Cases
• Ambient water surface (300 K)
• Supercooled water surface (200 K)
• Hexagonal ice surface (200 K)
• Amorphous solid (quenched) water surface (100 K)
• Starting point charge-neutral equilibrium
  surfaces
• Dynamic simulations of surface accommodation
• and final states
• Localization analysis

Á. Madarász, P. J. Rossky, L. Turi, JCP 126,
234707 (2007).
10
Interior and surface hydrated electrons at
liquid water/vacuum interfaces

• (meta)stable surface states at 200 K
• vs. spontaneous internal states at 300 K

Dz(t)
10 ps
11
Surface vs. Internal states
Internal state bulk hydrated electron Surface state supercooled water interface
300 K Simulation temperature 200 K
2.4 Å Radius of the electron 2.7 Å
-3.1 eV Ground state energy -2.6 eV
1.9 eV Spectral maximum 1.5 eV
16 Coordination number (lt5 Å) 10
12
Alternative surface states
fully reorganized -OH
partly reorganized from dangling -OH
restricted reorganization otherwise occupied -OH
partly reorganized -OH
Bulk Supercooled water interface Amorphous solid water interface ice Ih interface
Temperature 300 K 200 K 100 K 200 K
Electron radius 2.4 Å 2.7 Å 3.0 Å 2.6 Å
Ground state energy -3.1 eV -2.6 eV -1.6 eV -2.7 eV
Spectral maximum 1.9 eV 1.5 eV 1 eV 1.6 eV
13
Donor-Acceptor characterization of water molecules
1 AA 2 AD 3 DD 4 AD ice AADD
strong electron binding
Concept N. I. Hammer, J.-W. Shin, J. M.
Headrick, E. G. Diken, J. R. Roscioli,
G. H. Weddle, and M. A. Johnson, Science,
306, 675 (2004).
14
Hydrated electrons at solid water interfaces
Ice Ih, 200K

• H-bonding structure analysis
• AA (solid) and AAD (dashed)

AAD
AA
ASW, 100K
AAD
15
Equilibrium and non-equilibrium preparation of
cluster anions

• quenched clusters (QC)
• Prepare warm (ambient) neutral equilibrium
  structures
• ? quench them gradually to a sequence
  of lower Ts
• Cluster surface site analysis
• metastable clusters (MC)
• Alternative preparation protocol assemble the
  neutral clusters at very low T ? warm them up
  gradually to the desired higher T.
• metastable clusters have never seen annealing
  temperatures
• Add the electron and relax (for 200 ps).