Toward ab initio molecular dynamics modeling for sum-frequency generation spectra; an efficient algorithm based on surface-specific velocity-velocity correlation function

Abstract

Interfacial water structures have been studied intensively by probing the O-H stretch mode of water molecules using sum-frequency generation (SFG) spectroscopy. This surface-specific technique is finding increasingly widespread use, and accordingly, computational approaches to calculate SFG spectra using molecular dynamics (MD) trajectories of interfacial water molecules have been developed and employed to correlate specific spectral signatures with distinct interfacial water structures. Such simulations typically require relatively long (several nanoseconds) MD trajectories to allow reliable calculation of the SFG response functions through the dipole moment-polarizability time correlation function. These long trajectories limit the use of computationally expensive MD techniques such as ab initio MD and centroid MD simulations. Here, we present an efficient algorithm determining the SFG response from the surface-specific velocity-velocity correlation function (ssVVCF). This ssVVCF formalism allows us to calculate SFG spectra using a MD trajectory of only ∼100 ps, resulting in the substantial reduction of the computational costs, by almost an order of magnitude. We demonstrate that the O-H stretch SFG spectra at the water-air interface calculated by using the ssVVCF formalism well reproduce those calculated by using the dipole moment-polarizability time correlation function. Furthermore, we applied this ssVVCF technique for computing the SFG spectra from the ab initio MD trajectories with various density functionals. We report that the SFG responses computed from both ab initio MD simulations and MD simulations with an ab initio based force field model do not show a positive feature in its imaginary component at 3100 cm(-1).

Structure from Dynamics: Vibrational Dynamics of Interfacial Water as a Probe of Aqueous Heterogeneity

“…8,62,66,68 However, a recent study determined there is no positive peak at or below 3100 cm –1 and an apparent resonance appeared due to phase inaccuracy in measurements. 67,69 This is also confirmed by ab initio MD simulations 70−72 as well as force field MD simulations. 73,74 Regardless, the static phase-resolved SFG spectra of the water/air interface already reveal different structures of interfacial water when comparing the 3450 and 3700 cm –1 vibrational modes.…”

Communication: Vibrational sum-frequency spectrum of the air-water interface, revisited

“…17 In 2015, two new heterodyne-detected experiments with a more careful consideration of the reference used to determine the phase were performed by Yamaguchi, and Tahara and co-workers, which showed, in fact, that for neat H 2 O the low-frequency positive feature was absent 19,20 21 which does essentially confirm the result that there is no positive feature at low frequencies. We note that Nagata and co-workers have recently calculated sum-frequency spectra with ab initio MD simulations, 22 and Medders and Paesani have done the same 23 using their MB-pol model, 24 and the results of both groups are in good agreement with these new experiments.…”

Molecular Modeling of Water Interfaces: From Molecular Spectroscopy to Thermodynamics

“…30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 17 the nuclei from solvation effects such as the induced dipole and polarizability. 26 The SFG response can be expressed as:…”