Water graphene binding energy curve from diffusion Monte Carlo

Department of Earth Sciences & Department of Physics and Astronomy,

Thomas Young Centre@UCL & London Centre for Nanotechnology

University College London

Dario ALFÈAngelos Michaelides, Jie Ma, Enge Wang

Motivation

• Water-carbon (such as graphene, graphite and carbon nanotubes) interactions crucial to understand phenomena such as lubrication, heterogeneous ice nucleation, water formation on interstellar dust grain, structural and phase behaviour of water at the nanoscale, etc.

• Adsorption energy and structure of water monomers on any carbon surface is not well established, neither theoretically nor experimentally.

• Minute tuning of water-carbon potentials for nanotubes immersed in water can change filled tube to empty tubes.

• Small variations in the water-carbon potential leads graphite surfaces to appear as hydrophobic or hydrophilic.

Difficulties for water monomer geometry and adsorption energy

• Experiments: adsorption of water quickly results in water clusters

• Theory: – Quantum chemistry (MP2, CCSD(T), SAPT…) only available on

clusters; adsorption energy and geometry need to be extrapolated from acenes of various sizes, results in range 100 - 200 meV.

– Periodic DFT is inadequate, with predictions from repulsion (BLYP, B3LYP, revPBE) to binding energy of 150 meV (LDA).

Water on acenes

e.g. G. R. Jennes and K. D. Jordan, J. Phys. Chem. C, 113, 10242 (2009); Estimated binding energy is ~ 90 meV (SAPT)

Water-graphene binding curve from DFT

“Two leg” ~ 10 meV more stable than “One leg” with LDA (4 meV with PBE)

Water-Benzene binding curve

QuickTime™ and a decompressor

are needed to see this picture.

QMC technical details

• CASINO code: R. J. Needs, M. D. Towler, N. D. Drummond, P. Lopez-Rios, CASINO user manual, version 2.1, University of Cambridge, 2007.

• DF pseudopotentials (Trail and Needs, J. Chem. Phys. 122, 014112 (2005); ibid 122, 174109 (2005); see also CASINO web-page)

• Single particle orbitals from PWSCF (plane waves), 300 Ry PW cutoff. Then expanded in B-splines.

(D. Alfè  and M. J. Gillan, Phys. Rev. B, 70, 161101(R), (2004))

Water-Benzene binding curve

QuickTime™ and a decompressor

are needed to see this picture.

J. Ma, D. Alfè, A. Michaelides, E. Wang, JCP, 130, 154303 (2009)

Water-benzene binding energy: Nodal effects

ψ T (X) =eJ (X )D{φi (x j )}

Orbitals i from:

LDAB3LYPPBEPBE0HF

Best is LDA

Water-graphene binding curve

“Two leg” ~ 10 meV more stable than “One leg” with LDA (4 meV with PBE)

CASINO scaling on JaguarPF (Cray XT5, 150,000 cores at ONRL)