Advanced Simulation Methods SS 2018

A preliminary registration for this course is mandatory. Interested students should send an email to Maria Fyta as soon as possible. First meeting: Friday, April 13 at 11:30 in the ICP meeting room (Allmandring 3, 1st floor, room 1.095).

Overview

Type

Lecture and Tutorials (2 SWS in total)

Lecturer

Prof. Dr. Christian Holm, JP. Dr. Maria Fyta, Dr. Frank Uhlig, Dr. David Sean

Course language

English or German

Location

ICP, Allmandring 3; Room: ICP Meeting Room

Time

(see below)

The course will consist of three modules supervised by Prof. Dr. Christian Holm, Dr. Jens Smiatek, JP. Dr. Maria Fyta and will contain exercises, presentations, discussion meetings, and written reports, worked out in groups. Each group will have to give a talk for all modules. The students can work in groups. All groups should write a report on each module, which they should submit to the responsible person for each module by the deadline set for each module.

A preliminary registration for this course is mandatory. Interested students write an Email to Maria Fyta until TBA.

Module 1: Maria Fyta, Frank Uhlig, Inter-atomic interactions modeled with quantum mechanical simulations

Dates

First meeting: Friday, April 13 at 11:30 in the ICP meeting room (Allmandring 3, 1st floor, room 1.095).

Tutorials: TBA in the ICP CIP-Pool.

Talks: TBA am in the ICP meeting room.

Description

This module focuses on the influence of using quantum mechanical simulations. The quantum mechanical schemes which will be applied in this module are based on density functional theory (DFT). This method allows the investigation of the electronic properties of a system. An understanding of the method, an analysis of the results from the simulations is the main goal of this module. The analysis of the simulations should be written up in a report. The talk will be a presentation of a DFT-related journal paper. For this, one of the following papers can be chosen:

• Perspective: Advances and challenges in treating van der Waals dispersion forces in density functional theory, J. Klimeš and A. Michaelides, The Journal of Chemical Physics 137, 120901 (2012); doi: 10.1063/1.4754130
• Challenges for Density Functional Theory, A.J. Cohen, P. Mori-Sanchez, and W. Yang, Chemical Reviews 112, 289 (2012); dx.doi.org/10.1021/cr200107z.

Contact

If you have any questions regarding the organization or content of this module please do not hesitate to contact Maria Fyta. For practical guidance regarding the simulations Frank Uhlig.

Density functional theory and exchange-correlation functionals

Description

Many modern catalyses are performed using noble metals. In particular at the surface of these catalysts, which come in a multitude of shapes and chemical composition. The overall catalysis is determined by many factors, including the actual reactivity of chemical species at the surface, adsorption of reactants and desorption of products, as well as kinetics of the diffusion on the surface.

In this exercise you will look at the desorption behavior of hydrogen gas from the surface of noble metals. This process is important in the production of hydrogen gas for energy storage applications [1]. However, modeling this process using modern methods of quantum-mechanical density functional theory (DFT) is very challenging. Only very advanced and quite recent density functionals are able to describe the long-range dispersion interactions [2]. Hence, effective methods based on pair potentials have been developed. These methods can achieve comparable accuracy to more ab initio methods while coming at a signifcantly lower computational effort [3,4].

Your task is to develop such a pair-wise dispersion correction for the interaction of hydrogen gas with a metal surface. The first step is to understand and document the metallic behavior of your metal substrate, followed by investigation of the performance of common DFT functionals for the desorption process, and finally developing a dispersion correction by determining individual dispersion coefficients for the involved species [5].

[1] https://dx.doi.org/10.1038/ncomms6848

[2] https://dx.doi.org/10.1063/1.4754130

[3] https://dx.doi.org/10.1103/PhysRevLett.102.073005

[4] https://dx.doi.org/10.1063/1.3382344

[5] https://dx.doi.org/10.1063/1.2746031

[6] ASM tutorial info links

Literature

• A bird's-eye view of density-functional theory, Klaus Capelle, arXiv:cond-mat/0211443 (2002).
• Self-Consistent Equations Including Exchange and Correlation Effects, W. Kohn and L.J. Sham, , Phys. Rev. (140), A1133 (1965).
• Understanding and Reducing Errors in Density Functional Calculations, Min-Cheol Kim, Eunji Sim, and Kieron Burke, Phys. Rev. Lett. 111, 073003 (2013).
• An application of the van der Waals density functional: Hydrogen bonding and stacking interactions between nucleobases, V.R. Cooper, T. Thonhauser, and D.C. Langreth, J. Chem. Phys. 128, 204102 (2008).
• On the accuracy of density-functional theory exchange-correlation functionals for H bonds in small water clusters: Benchmarks approaching the complete basis set limit, B. Santra, A. Michaelides, and M. Scheffler, J. Chem. Phys. 127, 184104 (2007).
• On geometries of stacked and H-bonded nucleic acid base pairs determined at various DFT, MP2, and CCSD(T) levels up to the CCSD(T)/complete basis set limit level, I. Dąbkowska, P. Jurečka, and P. Hobza, J. Chem. Phys. 122, 204322 (2005).

Report

Please write a report 5-10 pages containing and discussing your results and hand it in by Friday TBA.

Module 2: Maria Fyta, Narayanan Krishnamoorthy Anand: Atomistic Simulations of Co-Solutes in Aqueous Solutions

Dates

First meeting: 18.05.2018 in the ICP meeting room.

Final meeting: 15.06.2018 in the ICP meeting room.

Deadline for reports: 15.06.2018

Description

This module focuses on atomistic Molecular Dynamics simulations and the study of biological co-solutes like urea, ectoine or hydroxyectoine and their influence on aqueous solutions. Biological co-solutes, often also called osmolytes are omnipresent in biological cells. A main function of these small-weight organic molecules is given by the protection of protein structures under harsh environmental conditions (protein stabilizers) or the denaturation of proteins (protein denaturants). The underlying mechanism leading to these effects is still unknown. It has been often discussed that osmolytes have a significant impact on the aqueous solution. The module consists of model development, simulation, analysis and oral and written presentation part.

Contact

If you have any questions regarding the organization or content of this module, please do not hesitate to contact Narayanan Krishnamoorthy Anand.

Part 1: Osmolytes and Kirkwood-Buff Theory

Description

This part introduces the students to the field of osmolyte research. An important theory to study solvation and binding behavior is given by the Kirkwood-Buff theory which can be well applied to computer simulations. The students should study the literature given below and present their findings. The presentation should at a minimum contain an introduction to Kirkwood-Buff theory in the context of the simulations.

Literature

• D. R. Canchi and A. E. Garcia, "Co-solvent effects on protein stability", Ann. Rev. Phys. Chem. 64. 273 (2013)
• J. G. Kirkwood and F. P. Buff. "The statistical mechanical theory of solutions. I." J. Chem. Phys. 19, 774 (1951)
• V. Pierce, M. Kang, M. Aburi, S. Weerasinghe and P. E. Smith, "Recent applications of Kirkwood–Buff theory to biological systems", Cell Biochem. Biophys. 50, 1 (2008)
• S. Weerasinghe and P. E. Smith, "A Kirkwood–Buff derived force field for sodium chloride in water", The Journal of Chemical Physics 119, 11342 (2003).
• J. Rösgen, B. M. Pettitt and D. W. Bolen, "Protein folding, stability, and solvation structure in osmolyte solutions", Biophys. J. 89, 2988 (2005)
• J. Smiatek, "Osmolyte effects: Impact on the aqueous solution around charged and neutral spheres", J. Phys. Chem. B 118, 771 (2014)
• T. Kobayashi et al, "The properties of residual water molecules in ionic liquids: a comparison between direct and inverse Kirkwood–Buff approaches", Phys.Chem.Chem.Phys. 19, 18924 (2017)

Part 2: Model Development and Simulations

Description

This part is practical. The simulations will be conducted by the software package GROMACS [1]. The students will develop Generalized Amber Force Fields (GAFF) [2] with the help of the ACPYPE program [3] for the osmolytes (urea, hydroxyectoine, ectoine) which will be used for the study of solvent properties like the thermodynamics of hydrogen bonding ans the diffusivity according to J. Phys. Chem. B 118, 771 (2014). In comparison to pure water, the students will analyze several water parameters and elucidate the differences in presence of osmolytes and their concentration dependent behavior. The Kirkwood-Buff theory will be used to calculate derivatives of the activity coefficients and the derivative of the chemical activity for the osmolytes.

Force Fields for ectoine and hydroxyectoine

• itp-File for Hydroxyectoine (7 KB)
• gro-File for Hydroxyectoine (682 bytes)
• itp-File for Ectoine (6 KB)
• gro-File for Ectoine (592 bytes)

Part 3: Tasks

1. Implement the developed force fields for the osmolytes (urea, ectoine and hydroxyectoine) in combination with the SPC/E water model. After energy minimization and warm up, run 20-30 ns simulations with GROMACS for osmolyte concentrations between c = 0 - 6 M.

2. Study the following properties for the different osmolytes and concentrations:

• diffusion coefficients
• hydrogen bond life times and number of hydrogen bonds for water-water, water-osmolyte and osmolyte-osmolyte pairs
• water mean relaxation times

Interpret the corresponding results. Are the molecules kosmotropes or chaotropes?

3. Calculate the radial distribution functions for all systems in terms of water-water, water-osmolyte and osmolyte-osmolyte pairs. Use this information to compute the

• Kirkwood-Buff integrals
• derivatives of the chemical activity
• derivatives of the activity coefficient

Interpret the corresponding results with regard to the findings in Biochemistry 43, 14472 (2004).

Literature

• D. van der Spoel, P. J. van Maaren, P. Larsson and N. Timneanu, "Thermodynamics of hydrogen bonding in hydrophilic and hydrophobic media", J. Phys. Chem. B 110, 4393 (2006)
• J. Wang, R. M. Wolf, J. W. Caldwell, P. A. Kollman and D. A. Case, "Development and testing of a general amber force field", J. Comp. Chem. 25, 1157 (2004)

Report

Please write a report of about 5 pages containing and discussing your results and hand it in until TBA.

Module 3: Christian Holm, Electrostatics, Lattice Boltzmann, and Electrokinetics

Dates

First meeting: TBA in the ICP meeting room.

Final meeting: TBA in the ICP meeting room.

Description

This module focuses on charged matter with electrostatic and hydrodynamic interactions. It should be taken in groups of three people. It consists of one lecture on electrostatic algorithms, simulations, theory, a presentation and a short report on the simulation results. You only have to give one common presentation and hand in one report. The Module 3 consists of three parts:

Contact

If you have any questions regarding the organisation or content of this module please do not hesitate to contact Christian Holm. For questions regarding the practical part of the module and technical help contact David Sean.

Part 1: Electrostatics

Description

This part is about the theory of electrostatic algorithms for molecular dynamics simulations. It is concerned with state of the art algorithms beyond the Ewald sum, especially mesh Ewald methods. To this end the students should read the referenced literature. Christian Holm will give an hour long lecture. Afterwards we will discuss the content and try to resolve open questions. The presentation should foster the students understanding of the P3M method as well as give them an overview of its performance compared to other modern electrostatics methods.

Literature

• C. Holm.
  "Simulating Long range interactions".
  Institute for Computational Physics, Universitat Stuttgart, 2018.
  [PDF] (15.4 MB)
  

• Markus Deserno, Christian Holm.
  How to mesh up Ewald sums. I. A theoretical and numerical comparison of various particle mesh routines.
  The Journal of Chemical Physics 109:7678, 1998.
  [PDF] (307 KB) [DOI]
• Axel Arnold, Florian Fahrenberger, Christian Holm, Olaf Lenz, Matthias Bolten, Holger Dachsel, Rene Halver, Ivo Kabadshow, Franz Gähler, Frederik Heber, Julian Iseringhausen, Michael Hofmann, Michael Pippig, Daniel Potts, Godehard Sutmann.
  Comparison of scalable fast methods for long-range interactions.
  Physical Review E 88(6):063308, 2013.
  [PDF] (2.3 MB) [DOI]
• Axel Arnold, Christian Holm.
  Efficient methods to compute long range interactions for soft matter systems.
  In Advanced Computer Simulation Approaches for Soft Matter Sciences II, pages 59–109. Edited by C. Holm, K. Kremer. Part of Advances in Polymer Science.
  Springer, Berlin, 2005. ISBN: 9783540260912.
  [PDF] (1.1 MB) [DOI]

Part 2: Electro-Osmotic Flow

Description

This part is practical. It is concerned with the movement of ions in an charged slit pore. It is similar to the systems that are discussed in the Bachelors thesis of Georg Rempfer which is recommended reading. A slit pore consists of two infinite charge walls as shown in the figure to the right. In this exercise you should simulate such a system with ESPResSo. You are supposed to use a Lattice Boltzmann fluid coupled to explicit ions which are represented by charge Week-Chandler-Anderson spheres. In addition to the charge on the walls, the ions are also subject to an external electrical field parallel to the walls. Electrostatics should be handled by the P3M algorithm with ELC. A set of realistic parameters and an more in detail description of the system can be found in the thesis. You should measure the flow profile of the fluid and the density and velocity profiles of the ions. The case of the slit pore can be solved analytically either in the case of only counter ions (the so called salt free case) or in the high salt limit (Debye-Hueckel-Limit). Calculate the ion profiles in one or both of these cases and compare the results with the simulation.

Instructions and Literature

Some ESPResSo tutorials can be helpful.

• General part and parts 4 & 6 of the Lattice-Boltzmann tutorial
• Part 7 of the charged systems tutorial to see how to setup proper electrostatics in quasi-2D geometry.

• Georg Rempfer, "Lattice-Boltzmann Simulations in Complex Geometries" (1.36 MB), 2010, Institute for Computational Physics, Stuttgart

Part 3: Electrophoresis of Polyelectrolytes

Description

In this part you simulate the movement of a charged polymer under the influence of an external electrical field and hydrodynamic interactions. Set up a system consisting of a charge polymer, ions with the opposite charge to make the system neutral and an Lattice Boltzmann fluid coupled the the ions and polymer. Apply an external field and measure the center of mass velocity of the polymer as a function of the length of the polymer for polymers of one to 20 monomers. Make sure the system is in equilibrium before you start the sampling. Compare your result to theory and experimental results (see literature).

Instructions and Literatur

General part and part 5 of Media:04-lattice_boltzmann.pdf

• Kai Grass, Ute Böhme, Ulrich Scheler, Hervé Cottet, Christian Holm.
  Importance of Hydrodynamic Shielding for the Dynamic Behavior of Short Polyelectrolyte Chains.
  Physical Review Letters 100(9):096104, 2008.
  [PDF] (115 KB) [DOI]
• Kai Christian Grass.
  Towards realistic modelling of free solution electrophoresis: a case study on charged macromolecules.
  PhD thesis, Goethe-Universität Frankfurt am Main, 2008.
  [PDF] (5.3 MB)

Report

At the final meeting day of this module, one group will give a presentation about the learned and performed work. In addition, they write a report of about 5 pages containing and discussing the obtained results and hand it in together with the reports of the other modules at the end of the course (see above).

The final report is due electronically Friday night, TBA