QTPIE charge model improves water dipole moments

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 ,[object Object],[object Object],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

[object Object],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? ,[object Object],[object Object],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

[object Object],[object Object],[object Object],[object Object],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 ,[object Object],[object Object],[object Object],Rappé, A. K.; Goddard, W. A. , J. Phys. Chem. 95 (1991), 3358-3363 .

Limitations of QEq ,[object Object],[object Object],[object Object],[object Object],voltage distance        

QTPIE, our new charge model ,[object Object],[object Object],J. Chen and T. J. Martínez , Chem. Phys. Lett. 438 (2007) 315 -3 20. voltage distance        

Features of QTPIE ,[object Object],[object Object],[object Object]

Dissocation of H 2 O in QEq and QTPIE ,[object Object],[object Object],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 ,[object Object],[object Object],[object Object],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 ,[object Object],[object Object],[object Object],[object Object],1 Jorgensen, W. L.; et al. , J. Chem. Phys. 79 (1983) 926-935.

New parameters for TIP3P/QTPIE and TIP3P/QEq ,[object Object],[object Object],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 ,[object Object],[object Object],[object Object],[object Object],[object Object],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 ,[object Object],planar twisted 4 4 3 14 No. of nonzero electrostatics parameters TIP3P/QTPIE TIP3P/QEq TIP3P AMOEBA Water model

Conclusions ,[object Object],[object Object],[object Object]

Acknowledgments ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

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 ,[object Object],[object Object],[object Object],twisted planar out of plane in plane dipole axis

QTPIE charge model improves water dipole moments

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QTPIE charge model improves water dipole moments