Abstract
In the present work, we provide an electronic structure based method for the “on-the-fly” determination of vibrational sum frequency generation (v-SFG) spectra. The predictive power of this scheme is demonstrated at the air-water interface. While the instantaneous fluctuations in dipole moment are obtained using the maximally localized Wannier functions, the fluctuations in polarizability are approximated to be proportional to the second moment of Wannier functions. The spectrum henceforth obtained captures the signatures of hydrogen bond stretching, bending, as well as low-frequency librational modes.
Highlights
Vibrational spectroscopy provides microscopic fingerprints of the structure and dynamics at the molecular level in condensed phase systems [1,2,3]
Ab initio molecular dynamics (AIMD) has proven to be extremely useful as the interatomic forces are obtained from accurate electronic structure calculations [10,11]
The net isotropic polarizability can be expressed as where Si is the spread of the ith Wannier center, NWF is the number of maximally localized Wannier functions (MLWFs), and β is a proportionality constant
Summary
Vibrational spectroscopy provides microscopic fingerprints of the structure and dynamics at the molecular level in condensed phase systems [1,2,3]. The success of simulations depends largely on the force field employed to describe the interatomic interactions In this regard, ab initio molecular dynamics (AIMD) has proven to be extremely useful as the interatomic forces are obtained from accurate electronic structure calculations [10,11]. An alternative representation, which is more suited for chemical problems, is provided by so-called maximally localized Wannier functions (MLWFs), i.e., wn (r − R) that are obtained by a unitary transformation of the Bloch orbitals [13,14] The construction of this Wannier representation enables to split the continuously varying total electronic density into contributions originating from localized fragments of the system. MLWFs are expressed as Molecules 2020, 25, 3939; doi:10.3390/molecules25173939 www.mdpi.com/journal/molecules
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