First principle calculations of dipole-dipole dispersion coefficients for the ground and first π → π∗ excited states of some azabenzenes

• The complex polarization propagator method has been applied to the calculation of dipole-dipole dispersion coefficients (also known as C6 coefficients) of pyridine, pyrazine, and s-tetrazine. These calculations refer to the electronic ground states as well as the first excited states of π → π∗ character. It is argued that accurate ground state dispersion coefficients are obtained with density functional theory using the B3LYP exchange-correlation functional. The proposed values for the C6 coefficients of pyridine, pyrazine, and s-tetrazine in their ground states are 1543 a.u., 1398 a.u., and 1014 a.u., respectively. Multi-configurational complete active space calculations are performed on these compounds in their respective π → π∗ excited state. The isotropic averages of the frequency-dependent polarizabilities are smaller in the excited states, but the effective frequencies-defined in the London-van der Waals dispersion relation-are on the other hand larger.

Ämnesord

NATURVETENSKAP  -- Kemi -- Teoretisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Theoretical Chemistry (hsv//eng)

Nyckelord

Density functional theory

Dispersions

Ground state

Pyridine

Van der Waals forces

Complete active space

Complex polarization propagator

Dispersion coefficient

Dispersion relations

Electronic ground state

Exchange-correlation functionals

First principle calculations

Frequency-dependent polarizabilities

Excited states

NATURAL SCIENCES

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