Frequency calculations using density functional theory (DFT) determine the normal modes of vibrations and the corresponding vibrational frequencies of a molecule or solid. These calculations are based on harmonic oscillations and the idea that minor deviations can describe the vibrational motions of atoms in a system from their equilibrium positions.
To perform a frequency calculation using DFT, the system's geometry is first optimized using DFT to find the equilibrium structure. Then the Hessian matrix (the matrix of second derivatives of the energy concerning the atomic coordinates) is calculated. The eigenvalues of this matrix correspond to the square of the vibrational frequencies, and the eigenvectors correspond to the normal modes of vibration.
Frequency calculations using DFT are widely used in computational chemistry and materials science to study the vibrational properties of molecules and solids. They can provide information about the vibrational spectra of a system, which can be compared with experimental measurements such as infrared and Raman spectroscopy.
As with geometry optimization, the accuracy of frequency calculations using DFT depends on the choice of the functional and the basis set used, as well as the computational cost.
To perform a frequency calculation using DFT, the system's geometry is first optimized using DFT to find the equilibrium structure. Then the Hessian matrix (the matrix of second derivatives of the energy concerning the atomic coordinates) is calculated. The eigenvalues of this matrix correspond to the square of the vibrational frequencies, and the eigenvectors correspond to the normal modes of vibration.
Frequency calculations using DFT are widely used in computational chemistry and materials science to study the vibrational properties of molecules and solids. They can provide information about the vibrational spectra of a system, which can be compared with experimental measurements such as infrared and Raman spectroscopy.
As with geometry optimization, the accuracy of frequency calculations using DFT depends on the choice of the functional and the basis set used, as well as the computational cost.
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