Hochgenaue Potentialhyperflächen und rovibronische Struktur von Malonaldehyd und CH4+ unter Berücksichtigung von Tunneleffekten

• Antragsteller: Professor Dr. David P. Tew
• Fachliche Zuordnung: Theoretische Chemie: Moleküle, Materialien, Oberflächen ; Theoretische Chemie: Elektronenstruktur, Dynamik, Simulation
• Förderung: Förderung von 2007 bis 2010
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 50479464

• Erstellungsjahr: 2010

Zusammenfassung der Projektergebnisse

Molecules are not static objects. They are continuously in motion, vibrating and sometimes reacting from one chemical species to another. A knowledge of how the energy changes as the nuclei move (i.e. the potential energy surface) is crucial to the understanding the chemistry of these dynamical processes. If we are able to compute the potential energy surface, we can then simulate the vibrational motion of the nuclei, determine reaction pathways and predict reaction rates. Every point on the potential energy surface corresponds to the energy of the molecule for a different configuration of the nuclei. To accurately compute the energy it is necessary to go far beyond the orbital picture, where each electron moves in the average electrostatic field of the other electrons, and to account for the way in which the motion of every electron is correlated to that of all the others. The dominant source of error in the standard approaches for computing the energy of the electrons in a molecule is the poor description of the correlation between two electrons when they closely approach one another. By building the physics of this interaction explicitly into the description of electron correlation, it was possible to essentially eliminate this source of error with almost no additional computational cost. Having worked with others to develop an efficient computer program (in turbomole) for this explicitly-correlated technique, applicable to both open- and closed-shell molecular systems, it is now possible to compute energies and potential energy surfaces reliably for much larger molecules than previously feasible. Malonaldehyde (C3 O2 H3 ) is one of the simplest molecules that undergoes an intermolecular hydrogen transfer reaction, which is an important process that takes place in many enzyme reaction pathways. The hydrogen transfer is significantly faster than expected on the basis of Newtonian mechanics because the dual wave-particle nature of the hydrogen nucleus allows it to tunnel through the reaction barrier. Calculations that capture this quantum dynamics require as input a potential energy surface for how the energy changes with respect to all possible arrangements of the atoms. Using the new explicitly-correlated method, it was possible to compute tens of thousands of energies, to provide an accurate and reliable 21 dimensional potential energy surface for malonaldehyde. The computed tunnelling splitting of the lowest vibrational energy levels was for the first time in complete agreement with experimental observation and the surface may now confidently be used to investigate how the O· · ·O and O–H stretching modes influence the rate of hydrogen transfer.

Projektbezogene Publikationen (Auswahl)

• A diagonal orbital-invariant explicitly-correlated coupled-cluster method, Chem. Phys. Lett. 452 326 (2008)
  D. P. Tew, W. Klopper and C. Hättig
  
• Full Dimensional Quantum Calculations of the Ground State Tunneling Splitting of Malonaldehyde Using an Accurate ab initio Potential Energy Surface, J. Chem. Phys. 128 224314 (2008)
  Y. Wang, B. J. Braams, S. Carter, D. P. Tew and J. M. Bowman
  
• Heat of formation of the HOSO2 radical from accurate quantum chemical calculations, J. Chem. Phys. 129 114308 (2008)
  W. Klopper, D. P. Tew, N. González-García and M. Olzmann
  
• Implementation of the full explicitly correlated coupled-cluster singles and doubles model CCSD-F12 with optimally reduced auxiliary basis dependence, J. Chem. Phys. 129 201103 (2008)
  A. Köhn, G. W. Richings and D. P. Tew
  
• Low energy hydrogenation products of extended π systems Cn H2x : A DFT search strategy, benchmarked against CCSD(T) and applied to C60 , J. Chem. Phys. 129 114303 (2008)
  A. Bihlmeier, D. P. Tew, and W. Klopper
  
• Quantitative quantum chemistry, Mol. Phys. 106 2107 (2008)
  T. Helgaker, W. Klopper and D. P. Tew
  
• Second order coalescence conditions of molecular wave functions, J. Chem. Phys. 129 014104 (2008)
  D. P. Tew
  
• Accurate coupled-cluster calculations of the reaction barrier heights of two CH3 + CH4 reactions, J. Phys. Chem. A 113 11697 (2009)
  W. Klopper, R. A. Bachorz, D. P. Tew, J. Aguilera-Iparraguirre, Y. Carissan and C. Hättig
  
• Assessment of basis sets for F12 explicitly-correlated molecular electronic-structure methods, Mol. Phys. 107 693 (2009)
  F. A. Bischoff, S. Wolfsegger, D. P. Tew and W. Klopper
  
• Atomization energies from coupled-cluster calculations augmented with explicitlycorrelated perturbation theory, Chem. Phys. 356 14 (2009)
  W. Klopper, B. Ruscic, D. P. Tew, F. A. Bischoff and S. Wolfsegger
  
• Non-IPR C60 solids, J. Chem. Phys. 130 164705 (2009)
  D. Löffler, N. Bajales, M. Cudaj, P. Weis, S. Lebedkin, A. Bihlmeier, D. P. Tew, W. Klopper, A. Böttcher and M. M. Kappes
  
• The geminal basis in explicitly-correlated wave functions, Chem. Phys. 356 25 (2009)
  S. Höfener, D. P. Tew, W. Klopper and T. Helgaker
  
• Accurate computational thermochemistry from explicitly correlated coupled-cluster theory, Theor. Chem. Acc.
  W. Klopper, R. A. Bachorz, C. Hättig and D. P. Tew
  
• Automated incremental scheme for explicitly correlated methods, J. Chem. Phys. 132 164114 (2010)
  J. Friedrich, D. P. Tew, W. Klopper and M. Dolg
  
• Explicitly correlated coupled-cluster theory. In: Recent Progress in Coupled Cluster Methods: Theory and Applications, P. Cársky, J. Pittner, and J. Paldus (Eds.), Springer
  D. P. Tew, C. Hättig, R. A. Bachorz and W. Klopper
  
• Open-shell explicitly correlated F12 methods, Mol. Phys. 108 315 (2010)
  D. P. Tew and W. Klopper
  
• Sub-meV accuracy in first-principles computations of the ionization potentials and electron affinities of the atoms H to Ne , Phys. Rev. A 81 022503 (2010)
  W. Klopper, R. A. Bachorz, D. P. Tew and C. Hättig
  
• Towards the Hartree-Fock and coupled-cluster singles and doubles basis set limit: A study of various models that employ single excitations into a complementary auxiliary basis set, J. Chem. Phys. 132 024101 (2010)
  A. Köhn and D. P. Tew
  
• Ab initio theory for accurate spectroscopic constants and molecular properties II. In: Handbook of High-Resolution Spectroscopies, F. Merkt and M. Quack (Eds.), John Wiley & Sons, Chichester
  D. P. Tew, W. Klopper, R. A. Bachorz and C. Hättig