PICVib: An accurate, fast, and simple procedure to investigate selected vibrational modes at high theoretical levels

Abstract

A new approach Procedure for Investigating Categories of Vibrations (PICVib) for estimating vibrational frequencies of selected modes using only the structure and energy calculations at a more demanding computational level is presented and explored. The PICVib has an excellent performance at only a small fraction of the computational demand required for a complete analytical calculation. The errors are smaller than ca. 0.5% when DFT functionals are combined with high level ab initio methods. The approach is general because it can use any quantum chemical program and electronic structure method. It is very robust because it was validated for a wide range of frequency values (ca. 20-4800 cm(-1)) and systems: XH(3) (D(3h) ) with X = B, Al, Ga, N, P, As, O, S, and Se, YH(4) (D(4h) ) with Y = C, Si, and Ge, conformers of RDX, S(N) 2 and E2 reactions, [W(dppe)(2)(NNC(5)H(10))] complex, carbon nanotubes, and hydrogen-bonded complexes including guanine-cytosine pair.

PICVib: an accurate, fast and simple procedure to investigate selected vibrational modes at high theoretical levels and evaluate Raman intensities

“…The theoretical formulation has been reported previously, and we intend to only present a brief review and some details of the PICVib extension for Raman intensity calculations. The basic assumption of the PICVib approach is the similarity between the normal mode coordinates determined at the lower and higher levels.…”

“…Thus, the development of approaches that can provide reliable Raman spectra using high‐level electronic structure methods for large and complex molecular systems is one of the most challenging and relevant goals of computational quantum chemistry. Aiming at these goals, we have proposed, implemented and tested an approach denoted as procedure for investigating categories of vibrations (PICVib) that is capable of providing fast and accurate results for vibrational wavenumbers and infrared intensities . This approach is quite simple to implement and to use because it basically involves the calculation of the vibrational infrared and Raman spectra using a low demanding method from which the normal modes of interest can be selected for a better description at a higher level.…”

“…Depending upon the choices, e.g. convergence criteria, iterative subspace size, preconditioner and quantum chemical method for calculating analytical gradients and analytical/numerical Hessians, the mode‐tracking approach can be more computationally intensive than the PICVib procedure, especially for Raman intensities with highly correlated methods . In addition, it requires (meta)programming, which is freely available (AKIRA code) for several computational quantum chemistry programs .…”

“…semiempirical, density functional based tight binding (DFTB) and density functional theory (DFT)) and can calculate single‐point molecular properties (energy, dipole moments and polarizabilities) at higher levels. The convergence to the analytical vibrational wavenumber and intensity is not necessarily guaranteed; however, there are some internal checks that can provide indications of the exactness of the calculation and the need to improve the lower level method …”

“…In this procedure, a low‐demanding feasible computational method (‘method2’) is employed in the analytical vibrational calculation at the equilibrium structure provided by a higher level quantum chemical method (‘method1’). This high‐level method is then used in single‐point energy, dipole and polarizability tensor calculations at displaced structures along a selected normal mode to provide its vibrational wavenumber, infrared intensity and Raman intensity at this high level. Such an approach is denoted as PICVib (method1 : method2).…”