Transferable Potential Function for Flexible H 2 O Molecules Based on the Single-Center Multipole Expansion

et al. 2022

J. Phys. Chem. B

A polarizable potential function describing the interaction between acetonitrile molecules is introduced. The molecules are described as rigid and linear, with three mass sites corresponding to the CH 3 group (methyl, Me), the central carbon atom (C), and the nitrogen atom (N). The electrostatic interaction is represented using a single-center multipole expansion as has been done previously for H 2 O [Wikfeldt et al., Phys. Chem. Chem. Phys. 15, 16542 (2013)], by including multipole moments from dipole up to and including hexadecapole, as well as anisotropic dipole−dipole, dipole−quadrupole, and quadrupole−quadrupole polarizability tensors. The model is free of point charges. The nonelectrostatic part is described in a pair-wise fashion by a Born−Mayer repulsion and damped dispersion attraction. The potential function is parameterized to fit the interaction energy of small (CH 3 CN) n , n = 2−6, clusters calculated using the PBE0 hybrid functional with an additional atomic many-body dispersion contribution. The parameterized potential function is found to compare well with results of the electronic structure calculations of dissociation curves for different dimer orientations and cohesive properties (the equilibrium volume, cohesive energy, and the bulk modulus) of the α-phase of acetonitrile crystal. The average value of the molecular dipole moment obtained in the α-phase is 5.53 D, corresponding to ca. 40% increase as compared to the dipole moment of an isolated acetonitrile molecule, 3.92 D. The calculated densities of solid and liquid acetonitrile turn out to be 8−10% higher than experimental values. This appears to be caused by an overestimate of the atomic many-body dispersion interaction in the density functional calculations used as input in the parametrization of the potential function.

Section: Form Of the Potential Functionmentioning

confidence: 99%

“…The spatial extent of these damping functions is described by a parameter g damping length. See the Supporting Information in this work and in refs and for more details.…”

Section: Form Of the Potential Functionmentioning

confidence: 99%

Polarizable Force Field for Acetonitrile Based on the Single-Center Multipole Expansion

Myneni

et al. 2022

J. Phys. Chem. B

“…36 The spatial extent of these damping functions are described by a parameter g -damping length. See the Supporting Information in references 28,37 for more details.…”

Section: Electrostatic Interactionsmentioning

confidence: 99%

Polarizable force field for acetonitrile based on the single-center multipole expansion

Myneni

et al. 2022

Preprint

A polarizable potential function describing the interaction between acetonitrile molecules is introduced. The molecules are described as rigid and linear with three mass sites corresponding to the CH3 group (methyl, Me), the central carbon atom (C), and the nitrogen atom (N). The electrostatic interaction is represented using a single center multipole expansion (SCME) as has been done previously for H2O [Wikfeldt et al., Phys. Chem. Chem. Phys. 15, 16542 (2013)], by including multipole moments from dipole up to and including hexadecapole, as well as anisotropic dipole-dipole, dipole-quadrupole and quadrupole-quadrupole polarizability tensors. The model is free of point charges. The non-electrostatic part is described in a pair-wise fashion by a Born-Mayer repulsion and damped dispersion attraction. The potential function is parameterized to fit the interaction energy of small (CH3CN)n, n=2-6, clusters calculated using the PBE0 hybrid functional with an additional many-body dispersion contribution. The parameterized potential function is found to compare well with results of the electronic structure calculations of dissociation curves for different dimer orientations and cohesive properties (the equilibrium volume, cohesive energy, and the bulk modulus) of the α-phase of acetonitrile crystal. The average value of the molecular dipole moment obtained in the α-phase is 5.53 D, corresponding to a ca. 40% increase as compared to the dipole moment of an isolated acetonitrile molecule, 3.92 D.

“…In this work, we provide that understanding based on recently developed polarizable many-body potentials as interaction models. Building on our recent studies, , we employ the quasi-harmonic approximation to account for nuclear quantum effects in the Helmholtz free energy by means of extensive and high-precision phonon calculations. We find that the MB-pol interaction model, whose short-range part is rooted in coupled-cluster calculations, yields the anomalous VIE of ice Ih in better agreement with the experimental reference value than DFT calculations with the PBE functional.…”

mentioning

confidence: 99%

“…In this work, calculations with different interaction models are performed, employing and extending the Atomic Simulation Environment (ASE) for interfacing their respective implementations. This includes the fixed-point-charge-based force fields q-TIP4P/F , (as available in LAMMPS), the polarizable force fields AMOEBA14 , (as implemented in TINKER), SCME/f, , and MB-pol (as implemented in the MBX package). − All-electron density functional theory (DFT) calculations with the PBE exchange-correlation functional are performed with the FHI-aims code, , using the same high-accuracy settings thoroughly verified and employed , for ice Ih in previous work (see the Supporting Information for details). The DFT calculations mimic proton disorder with a simulation cell containing 12 molecules .…”

mentioning

confidence: 99%

New Insights into the Volume Isotope Effect of Ice Ih from Polarizable Many-Body Potentials

Rasti

et al. 2022

J. Phys. Chem. Lett.

Self Cite

The anomalous volume isotope effect (VIE) of ice Ih is calculated and analyzed based on the quasi-harmonic approximation to account for nuclear quantum effects in the Helmholtz free energy. While a lot of recently developed polarizable many-body potential functions give a normal VIE contrary to experimental results, we find that one of them, MB-pol, yields the anomalous VIE in good agreement with the most recent high-resolution neutron diffraction measurementsbetter than DFT calculations. The short-range three-body terms in the MB-pol function, which are fitted to CCSD(T) calculations, are found to have a surprisingly large influence. A vibrational mode group decomposition of the zero-point pressure together with a hitherto unconsidered benchmark value for the intramolecular stretching modes of H2O ice Ih obtained from Raman spectroscopy data unveils the reason for the VIE: a delicate competition between the latter and the librations.