Density functional and ab initio investigation of S2N2 and (SN)2

- The SN dimer, (SN)2, has a considerable multireference character.
- The molecular structure of (SN)2 is a trapezoid.
- Most hybrid functionals poorly describe molecular properties of (SN)2.
- Old GGA functionals give qualitatively correct results for (SN)2.
- MS-CASPT2 can be an alternative to MRCI+Q.

Quantum chemical calculations were performed to calculate the molecular properties of the 1Ag state of disulfur dinitride, S2N2, and the 1A1 state of the SN dimer, (SN)2, using density functional theory (DFT) and ab initio methods. The molecular structure of (SN)2 is a trapezoid instead of a rectangle. Because the multireference character of (SN)2 is considerable, most hybrid DFTs poorly describe its molecular properties. In contrast, old generalized gradient approximations give qualitatively correct descriptions of the molecular properties of (SN)2. Multi-state second-order multiconfigurational perturbation theory gives results that are close to those from multireference configuration interaction with the Davidson correction. The multireference character should be considered when calculating the molecular properties of poly sulfur nitride systems.

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