title: Molecular quantum mechanical gradients within the polarizable embedding approach--application to the internal vibrational Stark shift of acetophenone.
abstract: We present an implementation of analytical quantum mechanical molecular gradients within the polarizable embedding (PE) model to allow for efficient geometry optimizations and vibrational analysis of molecules embedded in large, geometrically frozen environments. We consider a variational ansatz for the quantum region, covering (multiconfigurational) self-consistent-field and Kohn-Sham density functional theory. As the first application of the implementation, we consider the internal vibrational Stark effect of the C=O group of acetophenone in different solvents and derive its vibrational linear Stark tuning rate using harmonic frequencies calculated from analytical gradients and computed local electric fields. Comparisons to PE calculations employing an enlarged quantum region as well as to a non-polarizable embedding scheme show that the inclusion of mutual polarization between acetophenone and water is essential in order to capture the structural modifications and the associated frequency shifts observed in water. For more apolar solvents, a proper description of dispersion and exchange-repulsion becomes increasingly important, and the quality of the optimized structures relies to a larger extent on the quality of the Lennard-Jones parameters.
authors.affiliation: Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, Odense M, Odense DK-5230 Denmark.
authors.forename: Nanna Holmgaard
authors.initials: NH
authors.lastname: List
authors.affiliation: Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø-The Arctic University of Norway, N-9037 Tromsø, Norway.
authors.forename: Maarten T P
authors.initials: MT
authors.lastname: Beerepoot
authors.affiliation: Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, Odense M, Odense DK-5230 Denmark.
authors.forename: Jógvan Magnus Haugaard
authors.initials: JM
authors.lastname: Olsen
authors.affiliation: Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø-The Arctic University of Norway, N-9037 Tromsø, Norway.
authors.forename: Bin
authors.initials: B
authors.lastname: Gao
authors.affiliation: Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø-The Arctic University of Norway, N-9037 Tromsø, Norway.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Ruud
authors.affiliation: Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, Odense M, Odense DK-5230 Denmark.
authors.forename: Hans Jørgen Aagaard
authors.initials: HJ
authors.lastname: Jensen
authors.affiliation: Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, Odense M, Odense DK-5230 Denmark.
authors.forename: Jacob
authors.initials: J
authors.lastname: Kongsted
mesh_terms: D000098:Acetophenones / Q000737:chemistry*; D016880:Anisotropy; D003198:Computer Simulation; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry; D055672:Static Electricity; D014732:Vibration; D014867:Water / Q000737:chemistry
chemical_list: D000098:Acetophenones; D012997:Solvents; D014867:Water; C038699:acetophenone; D004121:Dimethyl Sulfoxide