Questions tagged [vibrations]
Questions concerning molecular and solid vibrational modes.
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Is it right to neglect very small imaginary frequencies?
I'm running a DFT optimization (B3LYP/def2-TZVP) and frequencies in ORCA for a molecule. And I get one or two very small (1-6 cm^-1) imaginary frequencies which corresponds to a slight bend of the ...
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Retrieving Translational and Rotational Modes
I'm doing some post-processing using the vibrational modes of a molecule to solve a linear system of equations, but I believe I need all the modes in order to have a single, well-determined solution. ...
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Discrepancy between numerical and transformed derivatives
This is related to a prior question of mine Derivatives with respect to user defined vibrational modes. While that one focuses on potential software to use for derivatives with respect to normal modes,...
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What do negative phonon frequencies signify?
Negative frequencies "in general" mean the direction of displacement is reverse to that in positive frequencies.
Does it mean two frequencies with opposite signs but the same magnitude give ...
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Is there a software that can do derivatives with respect to user defined vibrational modes?
I'm doing some property calculations that depend on a sum of derivatives of some quantity with respect to normal vibrational modes. I was hoping to find some physical intuition relating the type of ...
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Alternatives to VEDA 4 vibrational energy distribution analysis software?
Said software is useful when you need to assign the peaks in vibrational spectra to different vibrational modes found in a hessian calculation for a given molecule, as described in Jamróz, Michał H. “...
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What's the point of doing high accuracy spectroscopy calculations?
I am currently reading Dickenson et al. (2013) The Fundamental Vibration of Molecular Hydrogen.
I am trying to understand why this calculation is important for the field beyond basic scientific ...
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What is the largest system for which vibrationally resolved electronic spectra have been simulated using ML-MCTDH?
Multi-layer Multi-configuration time-dependent Hartree (ML-MCTDH) is a method widely used for simulation of vibrationally resolved electronic spectra that incorporate the coupling between vibrational ...
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Phonon Calculations and Vibrational Modes
The Raman spectrum of a material shows certain 'active' modes for which we get experimental signatures. Phonon calculations are mostly used to calculate vibrational modes.
How can we determine the ...
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Package for computing properties of excited vibrational states
We're starting to develop some calculations of the hyperfine parameters (electric field gradient, spin-rotation coupling, spin-spin coupling) with CFOUR, and we reached a limitation of the public ...
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How many non-redundant internal coordinates are needed for optimisation of linear molecule?
I have been working to implement optimisation in internal coordinates (for a transition state search software I am working on). However, the implementation details are almost always glossed over in ...
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