Loading in 2 Seconds...

Anion Electronic Structure and Correlated, One-electron Theory

Loading in 2 Seconds...

- By
**vega** - Follow User

- 119 Views
- Uploaded on

Download Presentation
## PowerPoint Slideshow about ' Anion Electronic Structure and Correlated, One-electron Theory' - vega

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

### Anion Electronic Structure and Correlated, One-electron Theory

J. V. Ortiz

Department of Chemistry and Biochemistry

Auburn University

www.auburn.edu/cosam/JVOrtiz

Workshop on Molecular Anions and Electron-Molecule Interactions in Honor of

Professor Kenneth Jordan

July 1, 2007

Park City, Utah

Funding

National Science Foundation

Defense Threat Reduction Agency

Acknowledgments- Symposium Organizers
- Jack Simons
- Brad Hoffman

- Auburn University
- Department of Chemistry and Biochemistry

- Auburn Coworkers

- UNAM Collaborators:
- Ana Martínez
- Alfredo Guevara

Deductive agenda:

Deduce properties of molecules from quantum mechanics

Calculate chemical data, especially if experiments are difficult or expensive

Inductive agenda:

Identify and explain patterns in structure, spectra, energetics, reactivity

Deepen and generalize the principles of chemical bonding

Quantum Chemistry’s MissionsG. N. Lewis

E. Schrödinger

Hartree Fock Theory

Hartree Fock Equations:

(Tkin + Unucl + JCoul - Kexch)φiHF ≡

F φiHF=εiHF φiHF

Same potential for all i:

core, valence, occupied, virtual.

εiHF includes Coulomb and exchange contributions to IEs and EAs

Electron Propagator Theory

Dyson Equation:

[F + ∑(εiDyson)]φiDyson = εiDyson φiDyson

Self energy, ∑(E): Energy dependent, nonlocal potential that varies for each electron binding energy

εiDyson includes Coulomb, exchange, relaxation and correlation contributions to IEs and EAs

φiDyson describes effect of electron detachment or attachment on electronic structure

One-electron EquationsDyson Orbitals (Feynman-Dyson Amplitudes)

- Electron Detachment (IEs)

φiDyson(x1) =

N-½∫ΨN(x1,x2,x3,…,xN)Ψ*i,N-1(x2,x3,x4,...,xN)

dx2dx3dx4…dxN

- Electron Attachment (EAs)

φiDyson(x1) =

(N+1)-½∫ Ψi,N+1(x1,x2,x3,...,xN+1)Ψ*N(x2,x3,x4,…,xN+1) dx2dx3dx4…dxN+1

- Pole strength

Pi = ∫|φiDyson(x)|2dx

0 ≤ Pi ≤ 1

Electron Propagator Concepts

Electron Correlation

Dyson Orbital

Canonical MO

Correlated Electron

Binding Energy

Orbital Energy

Integer Occupation

Numbers

Pole Strengths

Independent-Particle

Potential

Energy-dependent,

Self-Energy

Accuracy versus Interpretability

- Does electron propagator theory offer a solution to Mulliken’s dilemma?

The more accurate the

calculations become,

the more the concepts

vanish into thin air.

- R. S. Mulliken

Uracil versus Thymine

- Methyl group destabilizes π orbitals with large amplitudes at nearest ring atom
- Therefore, IE(T) < IE(U)
- Valid principles for substituted DNA bases, porphyrins and other organic molecules

A Self-Energy for Large Molecules: P3

- Neglect off-diagonal elements of Σ(E) in canonical MO basis: φiDyson(x) = Pi½φiHF-CMO(x)
- Partial summation of third-order diagrams
- Arithmetic bottleneck: oN4 (MP2 partial integral transformation)
- Storage bottleneck: o2v2 in semidirect mode
- Abelian, symmetry-adapted algorithm in G03

Formulae for ΣP3(E)

ΣP3pq(E) =

½Σiab <pi||ab><ab||qi> Δ(E)-1iab +

½Σaij <pa||ij>(<ij||qa> + Wijqa) Δ(E)-1aij +

½Σaij Upaij(E)<ij||qa>Δ(E)-1aij

where

Δ(E)-1pqr = (E + εp – εq – εr)-1

Wijqa = ½Σbc<bc||qa><ij||bc> Δ-1ijbc

+ (1-Pij)Σbk<bi||qk><jk||ba> Δ-1jkab

Upaij(E) = - ½Σkl<pa||kl><kl||ij> Δ(E)-1akl

- (1 – Pij) Σbk<pb||jk><ak||bi> Δ(E)-1bjk

P3 Performance

- 31 Valence IEs of Closed-Shell Molecules:

(N2,CO,F2,HF,H2O,NH3,C2H2,C2H4,CH4,HCN,H2CO)

MAD (eV) = 0.20 (tz)

- 10 VEDEs of Closed-Shell Anions:

(F-,Cl-,OH-,SH-,NH2-,PH2-,CN-,BO-,AlO-,AlS-)

MAD (eV) = 0.25 (a-tz)

- Arithmetic bottleneck: o2v3 for Wijqa
- Storage bottleneck: <ia||bc> for Wijqa

Invitation to Propagate

Input to Gaussian 03

# OVGF 6-311G** iop(9/11=10000)

P3 Electron Propagator for Water

0 1

O

H 1 0.98

H 1 0.98 2 105.

Available diagonal approximations for Σ(E):

Second order, Third order, P3, OVGF (versions A, B & C)

Nucleotides: Gaseous Spectra

- Nucleotides: phosphate-sugar-base DNA fragments
- Electrospray ion sources
- Magnetic bottle detection
- High resolution laser spectroscopy of ions, mass spectrometry
- Goal: predict photoelectron spectra of anionic nucleotides (vertical electron detachment energies or VEDEs)

Photoelectron Spectra of 2’-deoxybase 5’-monophosphate Anions

DAMP

Anomalous peak for dGMP

Base = adenine

DCMP

G: lowest IE

of DNA bases

Base = cytosine

DGMP

Base = guanine

Dyson orbitals for

lowest VEDEs:

phosphate or base?

DTMP

Base = thymine

L-S.Wang, 2004

Hydrogen Bonds: DGMP vs DAMP

- DGMP: G amino to Phosphate oxygen
- DAMP: Sugar hydroxy to Phosphate oxygen

Nucleotide Electronic Structure

- Phosphate anion reduces Base VEDEs by several eV
- Base also increases Phosphate VEDEs
- Therefore, Base and Phosphate VEDEs

are close

- Differential correlation effects are large
- Koopmans ordering is not reliable

A Simple, Renormalized Self-Energy: P3+

ΣP3+pq(E) =

½Σiab <pi||ab><ab||qi> Δ(E)-1iab +

[1+Y(E)]-1 ½Σaij<pa||ij>(<ij||qa> + Wijqa) Δ(E)-1aij + ½Σaij Upaij(E)<ij||qa>Δ(E)-1aij

where

Y(E) = {-½Σaij<pa||ij>Wijqa Δ(E)-1aij} {½Σaij<pa||ij><ij||qa> Δ(E)-1aij}-1

P3+ Performance

- 31 Valence IEs of Closed-Shell Molecules:

(N2,CO,F2,HF,H2O,NH3,C2H2,C2H4,CH4,HCN,H2CO)

MAD (eV) = 0.19 (tz), 0.19 (qz)

- 10 VEDEs of Closed-Shell Anions:

(F-,Cl-,OH-,SH-,NH2-,PH2-,CN-,BO-,AlO-,AlS-)

MAD (eV) = 0.11 (a-tz), 0.13 (a-qz)

Reactivity of Al3O3- with H2O

- Wang: first anion photoisomerization
- Jarrold: Al3O3-(H2O)n photoelectron spectra n=0,1,2
- Distinct profile for n=1
- Similar spectra for n=2 and n=0

Strong Initial State Correlation

- Need better reference orbitals for:

diradicaloids, bond dissociation, unusual bonding …

- Generate renormalized self-energy with approximate Brueckner reference determinant

A Versatile Self-Energy: BD-T1

- Asymmetric Metric:

(X|Y)=

<Brueckner|[X†,Y]+(1+T2)|Brueckner>

- Galitskii-Migdal energy =

BD (Brueckner Doubles, Coupled-Cluster)

- Operator manifold: f~a†aa=f3
- Discard only 2ph-2hp couplings

Applications of theBD-T1 Approximation

- Vertical Electron Detachment Energies of Anions: MAD=0.03 eV
- 1s Core Ionization Energies: MAD = 0.2%
- Valence IEs of Closed-Shell Molecules:

MAD = 0.15 eV

- IEs of Biradicaloids: MAD = 0.08 eV

Bowen’s Photoelectron Spectrum of NH4-

B: Mysterious low-VEDE peak

Not due to hot NH4-

Variable relative intensity

Another isomer of NH4-?

A: H- detachment

with vibrational

excitation of NH3

X: H-(NH3)

NH3 increases H- VEDE

X

B

x300

A

Computational Search: NH4- Structures

Hydride anion: H-

H-(NH3) constituents:

Ammonia molecule: NH3

Lewis: 1 electron pair

H nucleus has 1+ charge

Negative charge attracts

+ end of polar NH bond

Lewis: 3 electron pairs

shared in polar NH bonds

+ 1 unshared pair on N

→

Partial + charge on H’s

Partial – charge on N

Anion(molecule)

structure

accounts for

dominant peaks

Computational Search:What is the structure for the low-VEDE peak?

Idea: NH2-(H2) anion-molecule complex

Reject: spectral peak would be high-VEDE, not low

Idea: NH4- has 5 valence e- pairs

Deploy in 4 N-H bonds and 1 unshared pair

at the 5 vertices of a trigonal biprism or

square pyramid

Calculations find no such structures!

Instead, they spontaneously rearrange ….

….to a heretical structure!

Tetrahedral NH4- has 4

equivalent N-H bonds

Defies Lewis theory

Defies valence shell

electron pair

repulsion theory

Structure similar to that of NH4+

So where are the 2 extra electrons?

Structural Confirmation:Experiment and Theory

Predicted VEDEs from Electron Propagator Theory

for Anion(molecule) and Tetrahedral forms of NH4-

coincide with peaks from photoelectron spectrum

Dyson Orbitals for VEDEs of NH4-

H-(NH3) has 2 electrons

in hydride-centered orbital

with minor N-H delocalization.

VEDE is 1.07 eV

Tetrahedral NH4- has 2

diffuse electrons located

chiefly outside of NH4+ core.

VEDE is 0.47 eV

Double Rydberg Anions

- Highly correlated motion of two diffuse (Rydberg) electrons in the field of a positive ion (NH4+ , OH3+)
- United atom limit is an alkali anion: Na-
- Extravalence atomic contributions in Dyson orbitals

NH4-

OH3-

Calculated N2H7- Structures

- H-(NH3)2 anion-

molecule complex

- NH4-(NH3) anion-

molecule complex

with tetrahedral NH4-

- N2H7- with hydrogen bond (similar to N2H7+ )

N2H7- VEDEs and Dyson Orbitals

H-(NH3)2 has hydride centered Dyson orbital

EPT predicts 1.49 eV for VEDE

Peak observed in spectrum at 1.46 ± 0.02 eV

Dyson orbital concentrated near NH4-

EPT predicts 0.60 eV for VEDE

Peak observed at 0.58 ± 0.02 eV

Dyson orbital concentrated near 3 hydrogens

EPT predicts 0.42 eV for VEDE

Peak observed at 0.42 ± 0.02 eV

Assignment of N3H10-EBEs to Double Rydberg Anions

- (NH4-)(NH3)2 : 0.66 (Expt.) 0.68 (EPT)
- (N2H7-)(NH3) : 0.49 (Expt.) 0.49 (EPT)
- (N3H10-) : 0.42 (Expt.) 0.40 (EPT)

x800

Electron Pair Concepts: Old and New

Chemical bonds arise

from pairs of electrons

shared betweenatoms

G.N. Lewis

I. Langmuir

W.N. Lipscomb

Unshared pairs

localized on single atoms

affect bond angles

Molecular cations may

bind an e- pair peripheral

to nuclear framework:

Double Rydberg Anions

R.J. Gillespie

R.S. Nyholm

Electron Propagator Theory and Quantum Chemistry’s Missions

- Deductive, quantitative theory:

Prediction and interpretation enable dialogue with experimentalists requiring accurate data

- Inductive, qualitative theory:

Orbital formalism generalizes and deepens qualitative notions of electronic structure, relating structure, spectra and reactivity

Download Presentation

Connecting to Server..