QTPIE: A new charge model for arbitrary geometries and systems
Download as PPT, PDF0 likes547 views
1) QTPIE is a new charge model that accounts for polarization effects in molecular dynamics simulations through charge transfer and polarization-dependent interactions. 2) When implemented in the TIP3P water model (TIP3P/QTPIE), it correctly describes the dissociation of water molecules and predicts dipole moments in water chains better than previous charge equilibration methods. 3) However, TIP3P/QTPIE does not accurately capture polarizability, as it does not include out-of-plane polarizability and underestimates in-plane components.
QTPIE: A new charge model for arbitrary geometries and systems
- 1. 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
- 2. 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
- 3. 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
- 4. 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
- 5. 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
- 6. 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
- 7. 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 .
- 8. 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
- 9. 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
- 10. 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
- 11. 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
- 12. 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. +
- 13. 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.
- 14. 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
- 15. 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°)
- 16. Mean dipole moment per water planar
- 17. Mean dipole moment per water twisted
- 18. 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
- 19. 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
- 20. Acknowledgments Prof. Todd J. Martínez Martínez Group Funding from DOE DE-FG02-05ER46260 Poster Tonight 7:30-9:30 BCEC Exhibit Hall B2 #107
- 21. Out-of-plane polarizability per water planar
- 22. Out-of-plane polarizability per water twisted
- 23. In-plane polarizability per water planar
- 24. In-plane polarizability per water twisted
- 25. Dipole-axis polarizability per water planar
- 26. Dipole-axis polarizability per water twisted
- 27. 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