Relativistic
GVVPT2 Multireference Perturbation Theory Description of the Electronic
States of Y<sub>2</sub> and Tc<sub>2</sub>
Patrick K. Tamukong
Mark R. Hoffmann
Zhendong Li
Wenjian Liu
10.1021/jp409426n.s001
https://acs.figshare.com/articles/Relativistic_GVVPT2_Multireference_Perturbation_Theory_Description_of_the_Electronic_States_of_Y_sub_2_sub_and_Tc_sub_2_sub_/2319325
The multireference generalized Van
Vleck second-order perturbation theory (GVVPT2) method is used to
describe full potential energy curves (PECs) of low-lying states of
second-row transition metal dimers Y<sub>2</sub> and Tc<sub>2</sub>, with scalar relativity included via the spin-free exact two-component
(sf-X2C) Hamiltonian. Chemically motivated incomplete model spaces,
of the style previously shown to describe complicated first-row transition
metal diatoms well, were used and again shown to be effective. The
studied states include the previously uncharacterized 2<sup>1</sup>Σ<sub>g</sub><sup>+</sup> and
3<sup>1</sup>Σ<sub>g</sub><sup>+</sup> PECs of Y<sub>2</sub>. These states, together with 1<sup>1</sup>Σ<sub>g</sub><sup>+</sup>, are relevant to discussion of controversial results in the literature
that suggest dissociation asymptotes that violate the noncrossing
rule. The ground state of Y<sub>2</sub> was found to be X<sup>5</sup>Σ<sub>u</sub><sup>–</sup> (similar to Sc<sub>2</sub>) with bond length <i>R</i><sub>e</sub> = 2.80 Å, binding energy <i>D</i><sub>e</sub> = 3.12 eV, and harmonic frequency ω<sub>e</sub> = 287.2 cm<sup>–1</sup>, whereas the lowest 1<sup>1</sup>Σ<sub>g</sub><sup>+</sup> state of Y<sub>2</sub> was found to lie 0.67 eV above the quintet ground state and
had spectroscopic constants <i>R</i><sub>e</sub> = 3.21
Å, <i>D</i><sub>e</sub> = 0.91 eV, and ω<sub>e</sub> = 140.0 cm<sup>–1</sup>. Calculations performed on
Tc<sub>2</sub> include study of the previously uncharacterized relatively
low-lying 1<sup>5</sup>Σ<sub>g</sub><sup>+</sup> and 1<sup>9</sup>Σ<sub>g</sub><sup>+</sup> states (i.e., 0.70 and 1.84 eV
above 1<sup>1</sup>Σ<sub>g</sub><sup>+</sup>, respectively). The ground state of Tc<sub>2</sub> was found to be X<sup>3</sup>Σ<sub>g</sub><sup>–</sup> with <i>R</i><sub>e</sub> = 2.13 Å, <i>D</i><sub>e</sub> = 3.50
eV, and ω<sub>e</sub> = 336.6 cm<sup>–1</sup> (for the
most stable isotope, Tc-98) whereas the lowest <sup>1</sup>Σ<sub>g</sub><sup>+</sup> state, generally
accepted to be the ground state symmetry for isovalent Mn<sub>2</sub> and Re<sub>2</sub>, was found to lie 0.47 eV above the X<sup>3</sup>Σ<sub>g</sub><sup>–</sup> state of Tc<sub>2</sub>. The results broaden the range of demonstrated
applicability of the GVVPT2 method.
2014-02-27 00:00:00
15Σ
ω e
Y 2
GVVPT 2 method
2C
eV
spectroscopic constants Re
Relativistic GVVPT 2 Multireference Perturbation Theory Description
bond length Re
11Σ
31Σ
19Σ
PEC
Tc 2
isovalent Mn 2
X 3Σg state
ground state
frequency ω e
quintet ground state
Tc 2The multireference
ground state symmetry
uncharacterized 21Σ g