QTPIE: A minimal extension of Goddard's QEq model with correct dissociation

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Information about QTPIE: A minimal extension of Goddard's QEq model with correct dissociation

Published on June 16, 2008

Author: acidflask

Source: slideshare.net


Poster presented at the Fall 2007 ACS national meeting.

QTPIE: A minimal extension of Goddard’s QEq model with correct dissociation Jiahao Chen and Todd J. Martínez Department of Chemistry, Frederick Seitz Materials Research Laboratory, and the Beckman Institute University of Illinois at Urbana-Champaign 5 Dipole response of linear water chains QTPIE , our new charge model Polarization effects are important in classical • Charge-transfer with polarization current equilibration molecular dynamics simulations • Use parameters from single water molecule to model chains of waters • Voltage attenuates with increasing distance • Compared with gas phase experimental data10, ab initio (DF-LMP2/aug- • Structure of water improved when polarization is accounted for, cc-pVDZ), and AMOEBA11, a point polarizable dipole force field even if implicitly1 voltage • Needed to describe local environmental effects, e.g. hydration of Mean dipole moment per water chloride in water clusters2 η2 2.6 Planar ( /N)/Debye η2 OPLS/AA OPLS/FQ Non-polarizable force field Polarizable force field 2.5 distance AMOEBA DF-LMP2/aug-cc-pVDZ Features of QTPIE 2.4 TIP3P/QTPIE 3 How to represent explicit polarization? TIP3P • Correct dissociation limit for uncharged fragments TIP3P/QEq 2.3 • Minimally parameterized in terms of chemically meaningful quantities • Polarizable point dipole models (electronegativites and hardnesses) 2.2 • Can obtain results for electrostatic properties comparable to those from 2.1 more sophisticated force fields +q, α1 -q, α2 2.0 Dissocation of water in QEq and QTPIE Induced dipoles calculated from site polarizabilities • Correct asymptotics 1.9 gas phase (experimental) • Drude oscillator/charge-on-spring/shell models • Charge separation on OH fragment retained Number of water molecules, N 1.8 0 5 10 15 20 25 30 35 40 1.0 q/e Twisted 2.6 ( /N)/Debye 2.5 0.5 AMOEBA DF-LMP2/aug-cc-pVDZ charge -Q >> q charge q+Q mass m << M R/Å mass M-m 2.4 TIP3P/QTPIE TIP3P spring k 0.0 TIP3P/QEq • Electronegativity equalization/charge equilibration/fluctuating- 2.3 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 charge models QTPIE 2.2 ab initio -0.5 QEq 2.1 2.0 -1.0 Model polarization as a type of charge transfer QTPIE prediction improved over QEq without reoptimizing parameters 1.9 ab initio = DMA charges from CASSCF(6/4)/STO-3G wavefunction gas phase (experimental) Number of water molecules, N Cooperative polarization in water 1.8 0 5 10 15 20 25 30 35 40 chemical electro- atoms in TIP3P/QTPIE predicts dipoles well • Dipole moment of water increases from 1.854 Debye6 in gas phase to hardness screened negativity molecule Coulomb 2.95±0.20 Debye7 at r.t.p. liquid phase (inverse) electric electrical • Simpler, computationally cheaper, yet results comparable to AMOEBA interaction capacitance potential • Polarization enhances dipole moment circuits • Water models with implicit or no polarization can’t describe local electri- Water model AMOEBA TIP3P TIP3P/QEq TIP3P/QTPIE η1 No. of electrostatics parameters 14 3 4 4 cal fluctuations χ2 η2 Conclusions 0V • Distance-dependent electronegativity difference leads to correct asympot- 4 QEq , a typical fluctuating-charge model ic behavior of dissociating neutral fragments • Energy minimized with respect to charges subject to constraint on total • New TIP3P/QTPIE water model predicts dipole moments better than Creating a water model with QTPIE charge Q TIP3P/QEq • Replace implicit polarization in TIP3P8 by explicitly polarizable charges • TIP3P/QTPIE models polarization effects with results comparable to using QTPIE and QEq more expensive force fields • QTPIE, QEq implemented in TINKER • Screened Coulomb interactions Acknowledgments • Reparameterized to reproduce ab initio dipole moments and anisotropic polarizabilities of a single water molecule Prof. Todd J. Martínez • ab initio = DF-LMP2/aug-cc-pVDZ Martínez Group • s-type Slater orbitals New parameters for Funding from DOE DE-FG02-05ER46260 References TIP3P/QTPIE and TIP3P/QEq Limitations of QEq 1. Berendsen, H. J. C.; Grigera, J. R.; Straatsma, T. P. J. Phys. Chem. 91 • Mulliken electronegativities and Parr-Pearson hardnesses (1987) 6269-71. • No out-of-plane dipole polarizability 2. Stuart, S. J.; Berne, B. J. J. Phys. Chem. 100 (1996) 11934 -11943. • Overestimates in-plane dipole polarizability 3. Yu, H.; van Gunsteren, W. F. Comput. Phys. Commun. 172 (2005) 69- • Unphysical charge distributions predicted for non-equilibrium geometries 85. • Cause: no distance penalty for charge transfer 4. Rappé, A. K.; Goddard, W. A. J. Phys. Chem. 95 (1991) 3358-3363. Original4 Expt.9 eV QTPIE QEq 5. Chen, J.; Martínez, T. J. Chem. Phys. Lett. 438 (2007) 315-320. 4.528 4.960 5.116 7.176 χH 6. Lide, D. R. CRC Handbook of Chemistry and Physics, 73rd ed., 1992. η2 η2 8.741 8.285 8.125 7.540 χO 7. Gubskaya, A. V.;Kusalik, P. G. J. Chem. Phys. 117 (2002) 5290-5302. 13.890 10.125 10.125 12.844 ηH 8. Jorgensen, W. L.; et al., J. Chem. Phys. 79 (1983) 926-935. 13.364 20.680 20.680 12.157 ηO distance 9. NIST Webbook. 10. Murphy, W. F. J. Chem. Phys. 67 (1977) 5877-5882. 11. Ren, P.; Ponder, J. W. J. Phys. Chem. B 107 (2003) 5933-5947.

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