MALDONADO alejandro Fabian
congresos y reuniones científicas
The performance of DFT method in full relativistic calculations of NMR properties
Congreso; Tenth Triennial Congress of the World Association of Theoretical and Computational Chemists (WATOC); 2014
Institución organizadora:
Laboratorio de Química Teórica Computacional (QTC) Facultad de Química
Recent theoretical and computational developments of full relativistic formalisms give now the opportunity to calculate and analyze the electronic origin of magnetic molecular properties of heavy-atom containing molecules, and improve the understanding of such properties. Since its formal development fifty years ago, Kohn-Sham density functional theory (DFT) has become the most popular electronic structure method in computational physics and chemistry. The DFT basic premise establishes that all the intricate motions and pair correlations in a many-electron system are somehow contained in the total electron density alone. DFT is usually the method of choice for calculation of NMR properties in medium-size heavy-atom containing molecules because it includes electron correlation at an affordable computational cost. Some 2-component DFT and wave function based methods are available though not all of them were tested in Sn or Pb containing molecules. Only in nonrelativistic regime it gives reliable results compared with experimental ones but it is not good enough in relativistic calculations of NMR magnetic properties. This is because the functional used were developed in order to assess the study of medium-size heavy-atom containing molecules or to analyse NR-like electronic mechanisms that may explain tendences or absolute values of magnetic shieldings. It is, therefore, of interest to assess whether DFT is a valuable tool in quantitative predictions of Sn and Pb NMR properties. In this work we present calculations of NMR shieldings of Sn and Pb atoms in XY4-nZn (X = Sn, Pb; Y , Z = H, F, Cl, Br, I) and PbH4-nIn (n = 0, 1, 2, 3, 4) family of compounds with four-component functionals as implemented in the DIRAC code. We found that results of calculations with Relativistic Polarization Propagator Appoach at Random Phase Approximation level (RelPPA-RPA) are more reliable than the DFT ones. We carried out calculations of nuclear magnetic shieldings with different functionals (KT2, KT3, PBE0, B3LYP, BLYP and BP86) and we argue on why those DFT functionals must be modified in order to obtain better results of such parameter within the relativistic regime. There is a dependence among both, electron correlation and relativistic effects that should be introduced in the functionals. They were parameterized only within a nonrelativistic regime and so they are not able to introduce properly the relativistic effects.