Protons and Path Integrals Landmark Simulation of Condensed Phase - - PowerPoint PPT Presentation

Protons and Path Integrals

Landmark Simulation of Condensed Phase Proton Transfer Thomas Allen (PI: Nancy Makri)

Department of Chemistry University of Illinois

May 13, 2015

Thomas Allen (PI: Nancy Makri) May 13, 2015 1 / 20

Introduction

Charge transfer reactions are an important class of fundamental chemical reactions

Thomas Allen (PI: Nancy Makri) May 13, 2015 2 / 20

Introduction

Charge transfer reactions are an important class of fundamental chemical reactions A + B ⇀ ↽ A+ + B− AH + B ⇀ ↽ A− + BH+

Thomas Allen (PI: Nancy Makri) May 13, 2015 2 / 20

Introduction

Charge transfer reactions are an important class of fundamental chemical reactions A + B ⇀ ↽ A+ + B− AH + B ⇀ ↽ A− + BH+ These reactions are ubiquitous in biology Transfer of H, H+, and H− is a major synthetic motif Cutting-edge materials for energy storage and transport

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The Proton Transfer Problem

Proton transfer is a condensed phase process

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The Proton Transfer Problem

Proton transfer is a condensed phase process

• 10
• 5

5 10 15 20 0.8 1 1.2 1.4 1.6 1.8 kcal/mol Distance (Ang.) Gas Phase

Thomas Allen (PI: Nancy Makri) May 13, 2015 3 / 20

The Proton Transfer Problem

Proton transfer is a condensed phase process

• 10
• 5

5 10 15 20 0.8 1 1.2 1.4 1.6 1.8 kcal/mol Distance (Ang.)

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The Proton Transfer Problem

Proton transfer is a condensed phase process

• 10
• 5

5 10 15 20 0.8 1 1.2 1.4 1.6 1.8 kcal/mol Distance (Ang.)

Many degrees of freedom, transfering species is quantum mechanical Separation into interacting system and environment is key

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Quantum-Classical Approaches

Fundamental idea of quantum-classical separation has been around for many years

Thomas Allen (PI: Nancy Makri) May 13, 2015 5 / 20

Quantum-Classical Approaches

Fundamental idea of quantum-classical separation has been around for many years

Quantum Mechanics/Molecular Mechanics Surface Hopping Reduced Models (Spin-Boson, etc.)

Thomas Allen (PI: Nancy Makri) May 13, 2015 5 / 20

Quantum-Classical Approaches

Fundamental idea of quantum-classical separation has been around for many years

Quantum Mechanics/Molecular Mechanics Surface Hopping Reduced Models (Spin-Boson, etc.)

All of these methods make tradeoffs in rigor or representation We desire a rigorous method that works across many regimes of behavior

Thomas Allen (PI: Nancy Makri) May 13, 2015 5 / 20

Quantum-Classical Approaches

Fundamental idea of quantum-classical separation has been around for many years

Quantum Mechanics/Molecular Mechanics Surface Hopping Reduced Models (Spin-Boson, etc.)

All of these methods make tradeoffs in rigor or representation We desire a rigorous method that works across many regimes of behavior Capturing full system-bath interaction is especially important The Quantum-Classical Path Integral formalism is designed to achieve these goals

Thomas Allen (PI: Nancy Makri) May 13, 2015 5 / 20

QCPI in a Nutshell

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QCPI in a Nutshell

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QCPI in a Nutshell

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QCPI in a Nutshell

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QCPI Equations

ˆ ρred(s±

N ; N∆t) =

• dx±

N

• s+

N x+ N

• e−i ˆ

HN∆t/¯ h ˆ

ρ(0)ei ˆ

HN∆t/¯ h

s−

N x− N

• R. Lambert, N. Makri, J. Chem. Phys. 137, 22A552 and 22A553 (2012)

Thomas Allen (PI: Nancy Makri) May 13, 2015 10 / 20

QCPI Equations

ˆ ρred(s±

N ; N∆t) =

• dx±

N

• s+

N x+ N

• e−i ˆ

HN∆t/¯ h ˆ

ρ(0)ei ˆ

HN∆t/¯ h

s−

N x− N

• ˆ

ρred(s±

N ; N∆t) =

• dx0
• dp0 P(x0, p0)Q(s±

N , x0, p0; N∆t)

• R. Lambert, N. Makri, J. Chem. Phys. 137, 22A552 and 22A553 (2012)

Thomas Allen (PI: Nancy Makri) May 13, 2015 10 / 20

QCPI Equations

ˆ ρred(s±

N ; N∆t) =

• dx±

N

• s+

N x+ N

• e−i ˆ

HN∆t/¯ h ˆ

ρ(0)ei ˆ

HN∆t/¯ h

s−

N x− N

• ˆ

ρred(s±

N ; N∆t) =

• dx0
• dp0 P(x0, p0)Q(s±

N , x0, p0; N∆t)

• R. Lambert, N. Makri, J. Chem. Phys. 137, 22A552 and 22A553 (2012)

Thomas Allen (PI: Nancy Makri) May 13, 2015 10 / 20

The Azzouz-Borgis Model

Our goal is to extend previous work to treat atomistic systems

• H. Azzouz, D. Borgis, J. Chem. Phys. 98, 7361 (1993)

Thomas Allen (PI: Nancy Makri) May 13, 2015 11 / 20

The Azzouz-Borgis Model

Our goal is to extend previous work to treat atomistic systems A test system for our method should have several properties

Simple MD description Realistic interactions and energetics Rigorous approach is beneficial

• H. Azzouz, D. Borgis, J. Chem. Phys. 98, 7361 (1993)

Thomas Allen (PI: Nancy Makri) May 13, 2015 11 / 20

The Azzouz-Borgis Model

Our goal is to extend previous work to treat atomistic systems A test system for our method should have several properties

Simple MD description Realistic interactions and energetics Rigorous approach is beneficial

The Azzouz-Borgis model of proton transfer is just such a system

• H. Azzouz, D. Borgis, J. Chem. Phys. 98, 7361 (1993)

Thomas Allen (PI: Nancy Makri) May 13, 2015 11 / 20

The Azzouz-Borgis Model

• H. Azzouz, D. Borgis, J. Chem. Phys. 98, 7361 (1993)

Thomas Allen (PI: Nancy Makri) May 13, 2015 12 / 20

QCPI Challenges

ˆ ρred(s±

N ; N∆t) =

• dx0
• dp0 P(x0, p0)Q(s±

N , x0, p0; N∆t)

Thomas Allen (PI: Nancy Makri) May 13, 2015 13 / 20

QCPI Challenges

ˆ ρred(s±

N ; N∆t) =

• dx0
• dp0 P(x0, p0)Q(s±

N , x0, p0; N∆t)

Huge number of calculations required It is possible to parallelize these efficiently

Thomas Allen (PI: Nancy Makri) May 13, 2015 13 / 20

QCPI Challenges

ˆ ρred(s±

N ; N∆t) =

• dx0
• dp0 P(x0, p0)Q(s±

N , x0, p0; N∆t)

Thomas Allen (PI: Nancy Makri) May 13, 2015 14 / 20

QCPI Challenges

ˆ ρred(s±

N ; N∆t) =

• dx0
• dp0 P(x0, p0)Q(s±

N , x0, p0; N∆t)

Huge number of calculations required It is possible to parallelize these efficiently Forward-Backward paths must interface with MD

BW staff and LAMMPS developers helped incorporate this behavior efficiently

Thomas Allen (PI: Nancy Makri) May 13, 2015 15 / 20

QCPI Challenges

ˆ ρred(s±

N ; N∆t) =

• dx0
• dp0 P(x0, p0)Q(s±

N , x0, p0; N∆t)

Huge number of calculations required It is possible to parallelize these efficiently Forward-Backward paths must interface with MD

BW staff and LAMMPS developers helped incorporate this behavior efficiently

Further refinements suggested by BW staff

Using memory for file storage Investigating multi-level parallelism

Thomas Allen (PI: Nancy Makri) May 13, 2015 15 / 20

Results

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Results

Thomas Allen (PI: Nancy Makri) May 13, 2015 16 / 20

Results

Thomas Allen (PI: Nancy Makri) May 13, 2015 17 / 20

Future Directions

Complete converged anharmonic calculations Investigate bath ensemble properties Extending results to complex systems, including proteins and biomolecules

Although these systems are larger, their couplings may be more manageable

Thomas Allen (PI: Nancy Makri) May 13, 2015 18 / 20

Acknowledgements

Thomas Allen (PI: Nancy Makri) May 13, 2015 19 / 20