Download - Gold Clusters

-8-4048

121620242832364044

Au6(t) Au6(3d) Au6(p) Au6(dt)

Bare4PH35PH36PH3

Bare

4PH3

5PH3

6PH3

Au6(t) Au6(3d) Au6(p) Au6(dt)

-16-12-8-4048

121620

Au8(3d) Au8(h) Au8(s)

Bare4PH35PH36PH37PH3

Bare

4PH3

5PH3

6PH3

7PH3

Au8(3d) Au8(h) Au8(s)

-8

-4

0

4

Au4(b) Au4(t)

Bare

1PH3

2PH3

3PH3

Bare

1PH3

2PH3

3PH3

Au4(b) Au4(t)

En

erg

y (k

cal/

mol)

Isomers

Solvent and Ligand Influence on the Energetics and

Optical Transitions in Small Gold Clusters1Theoretical Division, 2Center for Nonlinear Studies, 3Center for Integrated Nano-Technologies, Los Alamos National Laboratory, New Mexico – 87545, 4NanoScience Technology Center, University of

Central Florida, Orlando, FL 32826The study of noble metal clusters holds promises for the great advances in materials science as they increasingly form the basis for assembly of nanoarchitectures having specific emergent properties. Recent progress in the synthesis of noble metal nanoclusters, for example, suggests that they will likely permit the manipulation of light at the molecular scale, if only their size and structure can be controlled at the atomic level. Experimental studies alone cannot fully address the fundamental questions about the cluster properties, and as such, theoretical studies can provide invaluable microscopic insight into the electronic structure and dynamics of these nanoclusters. Gold clusters and nanoparticles exhibit a rich array of important electronic, optical, chemical and catalytic properties, which has sparked a huge interest in gold-based systems in several interdisciplinary areas, leading to an explosive growth in the volume of both experimental and theoretical research.

Figure - The diatom: an example of biological blueprints for inorganic materials fabrication. To exploit biological specificity to produce highly fluorescent gold (Au) nanoclusters from soluble precursors by using peptide and protein templates to organize metal atoms into a highly ordered structure with novel optical properties.

Figure - Predictive design of noble metal nanoclusters. The iterative, a) synthesis, b) characterization (shown as fluorescence correlation spectroscopy), c) theoretical description (showing optical transitions mediated by the excited state dynamics), and d) applications testing of fluorescent metal nanoclusters.

LA-UR 09-03153

Au2 Au4(b) Au4(t) Au6(t) Au6(p)

Au6(dt) Au6(3d) Au8(s) Au8(h) Au8(3d)

1L

2L

3L

4L

5L

6L

Au6(t) Au6(p) Au6(dt) Au6(3d)

Geometries of four isomers of Au6 with ligand attachement from one (top) to full ligation (Last geometry in respective colums).

2.35

2.40

2.45

2.50

2.55

2.60

2.65

Au2 Au4(b) Au4(t) Au6(t) Au6(p) Au6(3d) Au6(dt) Au8(3d) Au8(h) Au8(s)

Bon

d L

ength

(Ǻ)

Gold Cluster

1L

2L

3L

4L

5L

6L

7L


2.50

2.55

2.60

2.65

2.70

2.75

2.80

2.85

2.90


Bon

d L

ength

(Ǻ)

Gold Cluster

Bare1L2L3L4L5L6L7L


Bond length variation between gold-gold and gold-ligand bonds in different isomers of small gold clusters, when ligands are attached starting from one to full ligation.

Au2

Au4(p)

G03

Total Energy (nm)-

270.917

-541.88

6

1st Transition Energy (nm) – GS

508.030

1049.390

NWChem

PBE0 B3LYP

DFT

Total Energy-

270.538

-541.28

3


624.775

1428.306

DFT-ZORA

Total Energy-

270.554

-541.31

4


625.771

1428.371

SODFT

Total Energy-

270.566

-541.34

4


620.456

1460.644

SODFT-ZORA

Total Energy-

270.581

-541.37

5


620.477

1460.890 Basis set with Polarization functional are required to investigate small gold clusters

with ligands. LANL2DZ reproduces the trends with one family of ligands. Ligands increase the energies and oscillator strengths of 1st transition of gold

clusters. Solvation effects partially simulate the effect of ligands on 1st transition energy for

bare clusters. For ligatedclusters solvation does not change 1st transition energy significantly but has a prominent effect on the oscillator strength.

Spin-orbit and ZORA relativistic effects do not significantly change energy for bare gold clusters considered.

Counter poise correction as well have small effect on energies (binding energy/mol).

Considered DFT functionals of different classes are consistent both qualitatively and quantitatively.

Ligand binding leads to the stabilization of more planar isomers of Au4 and Au6. No size scaling was revealed as judged by the 1st transition energy from Au2 to

Au8. Increase in number of ligands around the metal core reduces the metal-ligand

binding energy as expected. Ligands significantly effect the cluster geometries. Neutral gold clusters form stable bonds with primary and tertiary amine ligands,

which is in contrast to cationic gold cluster, which are stabilized with phosphenes only.

Number of ligands binding to a gold cluster largely depends upon cluster geometry.

Isomers of small gold clusters (Au2, Au4, Au6 and Au8)Relative energies for different isomers of small gold clusters with ligands. Comparison displays variations starting from saturated isomer with least number of ligands to the saturated siomer with most number of ligands. The lowest energy isomer is taken as reference structure (zero energy) for comparison.

DFT function

als

• SVWN5 • PBEPBE • TPSSTPS

S • B3LYP • CAM-

B3LYP

• LANL2DZ• LAN2DZ+

P• def2-SVP• def2-

TZVP• def2-

QZVP

• Gaussian 03/09

• Turbomol• NWChem

5.1

• Model -CPCM

• Solvent - Methanol

Basis Set

Solvation

Software

Theoretical Details

Excited State Properties - TDDFT

DFT Functional Binding Energy (kcal/ mol) Bond Lengths (A)

SVWN5 64.14 2.49PBEPBE 50.03 2.55TPSSTPSS 50.58 2.54

B3LYP 43.20 2.57CAM-B3LYP 41.62 2.55

Exp* 53.00 2.47

SVWN5 67.72 2.49PBEPBE 53.33 2.55TPSSTPSS 54.39 2.53B3LYP 41.14 2.57CAM-B3LYP 45.61 2.55

Solvated (Methanol)

Au2

Bonding energies and bond lengths of Au2 calculated with different (5 generations) DFT functionals compared with experimental data.

Representative geometries of Au2 and Au4 cluster with ligand attached as PMe3, (a) Au2(PMe3)2, (b) Au4(PMe3)2, (c) Au4(PMe3)4, (d) Au4(NMe3)4.

* Kordis et. al., Journal of Chemical Physics, 1974, 61, 5114.

-62

-52

-42

-32

-22

-12

NH3 NMe3 PH3 PMe3NH3 NMe3 PH3 PMe3

Au2L2

/ m

ol)

-62

-52

-42

-32

-22

-12


Au4L2

Ener

gy p

er Li

gand

(kc

al

-62

-52

-42

-32

-22

-12

NH3 NMe3 PH3 PMe3

SVWN5 PBETPSS B3LYPCAM-B3LYP

NH3 NMe3 PH3 PMe3

Au4L4

Bind

ing

Type of Ligand

-44

-39

-34

-29

-24

-19

-14


Au2L2

/ m

ol)

-44

-39

-34

-29

-24

-19

-14


Au4L2

Ener

gy p

er Li

gand

(kc

al

-44

-39

-34

-29

-24

-19

-14

NH3 NMe3 PH3 PMe3

LANL2DZ LANL2DZ-PSVP TZVPQZVP TZVP (sol)

NH3 NMe3 PH3 PMe3

Au4L4

Type of Ligand

Bind

ing

Binding energies per ligand in kcal/mol for geometries of Au2 and Au4 in partial and fully ligated forms determined using various DFT functionals (left, TZVP basis set has been used for all calculations) and various basis sets (right, TPSS functional has been used for all calculations).

BENCHMARKING

2.0

2.5

3.0

3.5

NH3 NMe3 PH3 PMe3 NH3 NMe3 PH3 PMe3

Au4L2

1.5

2.0

2.5

3.0

NH3 NMe3 PH3 PMe3

SVWN5PBEPBETPSSTPSSB3LYPCAM-B3LYP

NH3 NMe3 PH3 PMe3

Au4L4

3.0

3.5

4.0

4.5

5.0


Au2L2

2.0

2.5

3.0

3.5


Au4L2

1.5

2.0

2.5

3.0

NH3 NMe3 PH3 PMe3

SVWN5PBEPBETPSSTPSSB3LYPCAM-B3LYP

NH3 NMe3 PH3 PMe3

Au4L4

3.0

3.5

4.0

4.5

5.0


Au2L2

1st T

ran

siti

on

E

nerg

y (e

V)

Type of Ligand

SODFT and ZORA corrections for Au2 and Au4(p) bare clusters. Oscillator strengths for these cluster calculations are zero.

LUMO HOMO

Au2(NMe3)2

CAM-B3LYP =4.816 eV f=0.128

=0.96424

TPSS =4.407 eV f=0.000

=0.98933

Au4(PMe3)2

(Sol)

CAM-B3LYP =3.206 eV f=0.733

=0.94561

TPSS =2.700 eV f=0.003

=0.99798

Au4(NMe3)4

CAM-B3LYP =2.728 eV f=0.000

= 0.99137

TPSS =2.482 eV f=0.054

= 0.99336

Lowest energy state molecular orbitals for ligated Au2 and Au4 with CAM-B3LYP and TPSS. Figure showing different lowest states corresponding to the use of different DFT functionals for TDDFT absorption calculations.

Au2

Au4(t)

Au6(t)

Au8(d)

Au6(d)

Au6(d1)

Au4(p)

Au6(p)

Au8(t)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Au2 Au4 Au6 Au8Au2 Au4 Au6 Au8

Au6(t)

Au6(p)

Au6(dt)

Au6(3d)

Au2

Au4(b)

Au4(t)

Au8(3d)

Au8(s)

1st transition energy (eV) for geometries of Au2 and Au4 in partial and fully ligated forms determined using various DFT functionals with (right) and without solvent (left)

1st transition energy of several lowest energy isomers of small gold clusters (Au2-Au8)

Optical Properties

Geometry & Energetics