Anharmonic vibrational spectra from double incremental potential energy and dipole surfaces

Abstract

We extend the fragmentation-based double incremental expansion in FALCON coordinates (DIF) and its linear-scaling analogue [C. König and O. Christiansen, J. Chem. Phys., 2016, 145, 064105] to dipole surfaces. Thereby, we enable the calculation of intensities in vibrational absorption spectra from these cost-efficient property surfaces. We validate the obtained potential energy and dipole surfaces by vibrational spectra calculations employing damped response theory for correlated vibrational coupled cluster wave functions. Our largest calculation on a hexa-phenyl includes all 180 vibrational degrees of freedom of the system, which illustrates the potential of both the DIF schemes for property surface generation and the use of damped response theory from high-dimensional correlated vibrational wave functions. Generally, we obtain good agreement between the spectra calculated from the DIF property surfaces and the non-fragmented analogues. Moreover, when adopting suitable electronic structure methods, good agreement with respect to the experiment can be obtained, as shown for the example of 5-methylfurfural and RI-MP2. In conclusion, our results illustrate that the presented scheme with linearly scaling surfaces enables high quality spectra, as long as reasonably sized fragments can be defined. With this work, we push the realistic limits of vibrational spectra calculations from vibrational wave function methods and accurate electronic structure calculations to significantly larger systems than currently accessible.

The Structure of the “Vibration Hole” around an Isotopic Substitution—Implications for the Calculation of Nuclear Magnetic Resonance (NMR) Isotopic Shifts

“…Thus, a better approach is to treat the molecular potential non-perturbatively. Christiansen and co-workers [ 90 , 91 , 92 , 93 ] have developed methods to construct anharmonic potentials for polyatomic systems in an incremental fashion. However, for a molecule with 100 or more normal modes, these methods are not feasible.…”

Frozen-Density Embedding Based Many-Body Expansions

“…Such an MBE can be applied in combination with any quantum-chemical method and the individual quantum-chemical calculations can easily be performed in an embarrassingly parallel fashion (see, e.g., Refs. [42,43]).…”

Tailored multilevel approaches in vibrational structure theory: A route to quantum mechanical vibrational spectra for complex systems

“…Such full-space FALCON coordinates have further been combined with fragmentation schemes to allow the highly efficient generation of potential energy surfaces. [41,6] Moreover, the FALCON algorithm offers the possibility to successively enlarge the vibrational subspaces until a certain vibrational signature is converged. This so-called "growing scheme" has, for the harmonic case, been demonstrated for the amide-I vibrational frequencies of alpha-conotoxin, that is, a small natural oligopeptide.…”

“…Within the last years, however, the field has moved toward treating larger system sizes. For special cases, (correlated) vibrational structure calculations have been reported for thousands (hundreds) of degrees of freedom, [5,6] and even oligopeptides have been treated. [7,8] This, however, requires some sacrifices in the accuracy, both through the applied electronic structure method for the underlying potential energy surface and its expansion and through reduced vibrational spaces.…”