Loading in 2 Seconds...

Including the Effect of Solvent on Quantum Mechanical Calculations: The Continuum Model Approach

Loading in 2 Seconds...

148 Views

Download Presentation
##### Including the Effect of Solvent on Quantum Mechanical Calculations: The Continuum Model Approach

**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 - - - - - - - - - - - - - - - - - - - - - - - - - - -

**Including the Effect of Solvent on Quantum Mechanical**Calculations:The Continuum Model Approach**SOLVENT MODELS**• Classical Ensemble Treatments • Mixed QM/MM • Quantum Mechanical Reaction Fields**SOLVENT MODELS**• Classical Ensemble Treatments • Mixed QM/MM • Quantum Mechanical Reaction Fields • truncated electrostatics • complete electrostatics**SOLVENT MODELS**• Classical Ensemble Treatments • Mixed QM/MM • Quantum Mechanical Reaction Fields • truncated electrostatics • Onsager Sphere Method • complete electrostatics**SOLVENT MODELS**• Classical Ensemble Treatments • Mixed QM/MM • Quantum Mechanical Reaction Fields • truncated electrostatics • Onsager Sphere Method • Ellipsoidal Methods • complete electrostatics**SOLVENT MODELS**• Classical Ensemble Treatments • Mixed QM/MM • Quantum Mechanical Reaction Fields • truncated electrostatics • Onsager Sphere Method • Ellipsoidal Methods • SAM1 • complete electrostatics**SOLVENT MODELS**• Classical Ensemble Treatments • Mixed QM/MM • Quantum Mechanical Reaction Fields • truncated electrostatics • Onsager Sphere Method • Ellipsoidal Methods • SAM1 • complete electrostatics • polarizable continuum model (PCM)**SOLVENT MODELS**• Classical Ensemble Treatments • Mixed QM/MM • Quantum Mechanical Reaction Fields • truncated electrostatics • Onsager Sphere Method • Ellipsoidal Methods • SAM1 • complete electrostatics • polarizable continuum model (PCM) • isodensity PCM**SOLVENT MODELS**• Classical Ensemble Treatments • Mixed QM/MM • Quantum Mechanical Reaction Fields • truncated electrostatics • Onsager Sphere Method • Ellipsoidal Methods • SAM1 • complete electrostatics • polarizable continuum model (PCM) • isodensity PCM • conductor-like PCM**Onsager**Self-Consistent Reaction Field (SCRF) Volume of sphere chosen based on molecular volume**Implementation of Onsager SCRF Method**Wong - Wiberg - Frisch 1991-1992 Analytical First and Second Derivatives • Molecular Geometries • Vibrational Frequencies Fast, but Limited • Molecules that are not spheres? • Other solvent-solute interaction?**Furfuraldehyde conformational equilibrium**Which isomer is more stable? How much more stable?**Furfuraldehyde conformational equilibrium**Which isomer is more stable? How much more stable? Syn - Anti [kcal/mol] Onsager* Expt. Gas phase +0.93 +0.82 dimethyl ether (-120) -0.13 -0.58 *Theoretical model is RHF/6-31+G(d)//RHF/6-31G(d) gas phase geometry**Furfuraldehyde conformational equilibrium**Which isomer is more stable? How much more stable? Syn - Anti [kcal/mol] Onsager* Expt. Gas phase +0.93 +0.82 dimethyl ether (-120) +0.22 -0.58 *Theoretical model is B3LYP/6-31+G(d)//RHF/6-31G(d) gas phase geometry**Dipole formula can be generalized for**higher-order electrostatic terms:**Furfuraldehyde conformational equilibrium**Syn - Anti [kcal/mol] Spherical Cavity Dipole -0.13 Quadrupole -0.75 Octapole +0.29 Hexadecapole +0.42 Expt -0.58 Solvent is dimethylether**Rivail and Rinaldi (QCPE 1992)**• Extended to ellipsoidal cavity shape • used VDW radii to determine • sixth-order electrostatics • first derivatives**Rivail and Rinaldi (QCPE 1992)**• Extended to ellipsoidal cavity shape • used VDW radii to determine • sixth-order electrostatics • first derivatives 2-nitrovinylamine rotational barrier: E Form Z form**Rivail and Rinaldi (QCPE 1992)**TS E Form Z form**Rivail and Rinaldi (QCPE 1992)**2-nitrovinylamine rotational barrier: Solvent is N,N-dimethylformamide**What if our molecule is not in the**shape of a basketball or football?**Isodensity Polarizable Continuum Model**Keith - Foresman - Wiberg - Frisch (JPC 1996) • Cavity surface defined as an isodensity of the solute • 0.0004 is used because it gives expt molecular volumes • Solute is polarized by the solvent • represented by point charges on cavity surface • Self-Consistent Solution is found: • cavity changes each macroiteration**Furfuraldehyde conformational equilibrium**Model is B3LYP/6-31+G(d)//HF/6-31G(d) gas**Really two problems here:**1. Experiment is Free Energy, calculation includes only solute-solvent electrostatic interaction. 2. Hydrogen Bonding**Pisa Polarizable Continuum Model (PCM)**Miertus - Tomasi - Mennucci - Cammi (1980-present) • Cavity based on overlapping spheres centered on atoms • Free Energy Terms built in as solvent parameters • cavitation energy • dispersion energy • repulsion energy • Specialized Surface Charge Schemes • patches for interface regions**Conductor Polarizable Continuum Model (CPCM)**Barone - Cossi ( JPCA 1998) • Extension of Pisa Model • More Appropriate for Polar Liquids • electrostatic potential goes to zero on the surface • Specialized Surface Charge Schemes • patches for interface regions**Conductor Polarizable Continuum Model (CPCM)**Barone - Cossi ( JPCA 1998) Free Energies of Hydration: CPCM Model; basis set is 6-31G(d); TSNum=60; gas phase geometries; Barone & Cossi, JPCA 1998.**Conductor Polarizable Continuum Model (CPCM)**Barone - Cossi ( JPCA 1998) Free Energies of Hydration: Not Obvious How to determine radii of spheres Problem: Cavity tied to Method CPCM Model; basis set is 6-31G(d); TSNum=60; gas phase geometries; Barone & Cossi, JPCA 1998.**SUMMARY**Isodensity Methods better for determining cavity without parameterization Pisa model parameters useful when non-electrostatic terms are important In Progress: Merging the two methods**Menschutkin Reaction:**Is this reaction endothermic or exothermic?**Menschutkin Reaction:**Is this reaction endothermic or exothermic? What is the activation energy and mechanism?**Menschutkin Reaction:**Is this reaction endothermic or exothermic? What is the activation energy and mechanism? How does solvent influence this?**4-aminobenzonitrile**4ABN 4-dimethylaminobenzonitrile 4DMABN**Thanks**• AEleen Frisch • Ken Wiberg, Yale University • Mike Frisch, Gaussian Inc. • Todd Keith, SemiChem • Hans Peter Luthi, ETH Zurich • Brian Williams, Bucknell Univeristy