QTPIE: A new charge model for arbitrary geometries and systems
Upcoming SlideShare
Loading in...5
×
 

QTPIE: A new charge model for arbitrary geometries and systems

on

  • 2,102 views

Slides for my talk at the 234th ACS National Meeting (Fall 2007) in Boston, MA.

Slides for my talk at the 234th ACS National Meeting (Fall 2007) in Boston, MA.

Statistics

Views

Total Views
2,102
Views on SlideShare
2,093
Embed Views
9

Actions

Likes
0
Downloads
7
Comments
0

3 Embeds 9

http://www.slideshare.net 5
http://www.linkedin.com 3
https://www.linkedin.com 1

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

QTPIE: A new charge model for arbitrary geometries and systems QTPIE: A new charge model for arbitrary geometries and systems Presentation Transcript

  • QTPIE: A new charge model for arbitrary geometries and systems Jiahao Chen and Todd J. Martínez Department of Chemistry and the Beckman Institute Poster: 7:30-9:30 tonight, BCEC Exhibit Hall B2, #107
  • Polarization effects are important in classical molecular dynamics
    • Structure of water improved when polarization is accounted for, even if implicitly 1
    • Needed to describe local environmental effects, e.g. hydration of chloride in water clusters 2
    1 Berendsen, H. J. C.; Grigera, J. R.; Straatsma, T. P. J. Phys. Chem. 91 , 1987 , 6269-71. 2 Stuart, S. J.; Berne, B. J. J. Phys. Chem. 100 , 1996 , 11934 -11943. OPLS/AA Non-polarizable force field TIP4P/FQ Polarizable force field
    • Polarizable point dipole models
    How to represent explicit polarization in classical MD? Review: Yu, H.; van Gunsteren, W. F.; Comput. Phys. Commun. 172 (2005), 69-85. +q ,   -q ,   Induced dipoles calculated from site polarizabilities  fixed calculated
  • How to represent explicit polarization in classical MD?
    • Polarizable point dipole models
    • Drude oscillator/charge-on-spring/shell models
    Review: Yu, H.; van Gunsteren, W. F.; Comput. Phys. Commun. 172 (2005), 69-85. spring k charge -Q >> q mass m << M charge q+Q mass M-m calculated
    • Polarizable point dipole models
    • Drude oscillator/charge-on-spring/shell models
    • Electronegativity equalization/charge equilibration/fluctuating-charge models
      • Model polarization as a type of charge transfer
    How to represent explicit polarization in classical MD? Review: Yu, H.; van Gunsteren, W. F.; Comput. Phys. Commun. 172 (2005), 69-85. calculated
  • Fluctuating-charge models map molecules onto electrical circuits screened Coulomb interaction chemical hardness electro- negativity molecule More electropositive More electronegative 0 V         - Voltage + electric potential (inverse) capacitance electrical circuits Coulomb interaction
  • QEq, a typical fluctuating-charge model
    • Energy minimized with respect to charges subject to constraint on total charge Q
    • Screened Coulomb interactions
    • s -type Slater orbitals
    Rappé, A. K.; Goddard, W. A. , J. Phys. Chem. 95 (1991), 3358-3363 .
  • Limitations of QEq
    • No out-of-plane dipole polarizability
    • Overestimates in-plane dipole polarizability
    • Unphysical charge distributions predicted for non-equilibrium geometries
    • Cause: no distance penalty for charge transfer
    voltage distance        
  • QTPIE, our new charge model
    • Charge-transfer with polarization current equilibration
    • Voltage attenuates with increasing distance
    J. Chen and T. J. Martínez , Chem. Phys. Lett. 438 (2007) 315 -3 20. voltage distance        
  • Features of QTPIE
    • Correct dissociation limit for uncharged fragments
    • Minimally parameterized in terms of chemically meaningful quantities (electronegativites and hardnesses)
    • Can obtain results for electrostatic properties comparable to those from more sophisticated force fields
  • Dissocation of H 2 O in QEq and QTPIE
    • Correct asymptotics
    • Charge separation on OH fragment retained
    equilibrium geometry R QEq QTPIE ab initio QTPIE prediction improved over QEq without reoptimizing parameters ab initio = DMA charges from CASSCF(6/4)/STO-3G wavefunction
  • Cooperative polarization in water
    • Dipole moment of water increases from 1.854 Debye 1 in gas phase to 2.95±0.20 Debye 2 at r.t.p. liquid phase
    • Polarization enhances dipole moments
    • Water models with implicit or no polarization can’t describe local electrical fluctuations
    1 D. R. Lide, CRC Handbook of Chemistry and Physics , 73rd ed., 1992 . 2 A. V. Gubskaya and P. G. Kusalik, J. Chem. Phys. 117 (2002) 5290-5302. +
  • Creating a water model with QTPIE
    • Replace implicit polarization in TIP3P 1 by explicitly polarizable charges using QTPIE and QEq
    • QTPIE, QEq implemented in TINKER
    • Reparameterized to reproduce ab initio dipole moments and anisotropic polarizabilities of a single water molecule
      • ab initio = DF-LMP2/aug-cc-pVDZ
    1 Jorgensen, W. L.; et al. , J. Chem. Phys. 79 (1983) 926-935.
  • New parameters for TIP3P/QTPIE and TIP3P/QEq
    • Mulliken electronegativities and
    • Parr-Pearson hardnesses
    1 Rappé, A. K.; Goddard, W. A. , J. Phys. Chem. 95 (1991), 3358-3363. 2 Calculated from ionization potentials and electron affinities in NIST Webbook. 12.157 20.680 20.680 13.364   12.844 10.125 10.125 13.890   7.540 8.125 8.285 8.741   7.176 5.116 4.960 4.528   Expt. 2 QEq QTPIE Original 1 eV
  • Dipole response of linear water chains
    • Use parameters from single water molecule to model chains of water molecules
    • Compared with:
      • Gas phase experimental data 1
      • Ab initio DF-LMP2/aug-cc-pVDZ
      • AMOEBA 2 , a point polarizable dipole force field
    1 Murphy, W. F. J. Chem. Phys. 67 , 1977 , 5877-5882. 2 Ren, P.; Ponder, J. W. J. Phys. Chem. B 107 , 2003 , 5933-5947.. planar (0° twist) twisted (90°)
  • Mean dipole moment per water planar
  • Mean dipole moment per water twisted
  • TIP3P/QTPIE predicts dipoles well
    • Simpler, yet comparable to AMOEBA
    planar twisted 4 4 3 14 No. of nonzero electrostatics parameters TIP3P/QTPIE TIP3P/QEq TIP3P AMOEBA Water model
  • Conclusions
    • Distance-dependent electronegativity difference leads to correct asympotic behavior of dissociating neutral fragments
    • New TIP3P/QTPIE water model predicts dipole moments better than TIP3P/QEq
    • TIP3P/QTPIE models polarization effects with results comparable to more expensive force fields
  • Acknowledgments
    • Prof. Todd J. Martínez
    • Martínez Group
    • Funding from DOE DE-FG02-05ER46260
    • Poster
    • Tonight 7:30-9:30
    • BCEC Exhibit Hall B2
    • #107
  • Out-of-plane polarizability per water planar
  • Out-of-plane polarizability per water twisted
  • In-plane polarizability per water planar
  • In-plane polarizability per water twisted
  • Dipole-axis polarizability per water planar
  • Dipole-axis polarizability per water twisted
  • TIP3P/QTPIE doesn’t predict polarizabilities well
    • Identical to TIP3P/QEq
    • No out of plane polarizability
    • In-plane components underestimated
    twisted planar out of plane in plane dipole axis