1. Ab initio calculations of the ground and excited states of the ZnTe molecule and its ions
Professor : Ourida OUAMERALI
Laboratoire de chimie théorique ,computationnelle et photonique
Faculté de chimie , USTHB, Algiers, Algeria.
Algeria

2. Results and discussion Conclusion and prospects
Plan
Introduction 1
Theoretical approach 2
Results and discussion 3
Conclusion and prospects 4

3. Introduction:
The optical properties of the materials are a promising research areas, both theoretically and experimentally.
ZnTe is one of these materials that exhibit interesting optoelectronic properties. It can be employed in the detection and the generation of terahertz (THZ) radiation, leading to applications in several fields such as radiology.

4. M.Kurban and ¸ S. Erkoç, Journal of Computational and Theoretical
As a nono cristal, Zinc telluride (ZnTe) has been a subject of many experimental and theoretical investigations.
In the molecular state, some theoretical studies of that compound are reported, in which structural and energetic properties, especially of the fundamental state were investigated by Sakir ERKOC, Rengin Pekoz, and Mustafa Kurban.
R Pekoz, S Erkoç ,Physica,
E 40, 2921 (2008).
M.Kurban and ¸ S. Erkoç, Journal of Computational and Theoretical
Nanoscience Vol. 12, 2605–2615, (2015).

5. Problematic
Determination of different states of ZnTe as well as its ions ZnTe+ and ZnTe- using electronic spectroscopy.

6. Theoretical Approach Post HF HF TDDFT MP2 CCSD(T) HF Codes Calculation
Post HF (Exited state)
TDDFT
CASSCF
B3LYP
Heavy atoms
LANL2DZ
ECP28MWB
ECP46MWB

7. Results & discussion

8. EA cation ˃ EA neutral ˃ EA anion
Energetic Gap, Ionization potential and Electron affinity
Table 1 : Energetic Gap ΔE, Ionization Potential (IP) and Electron Affinity (EA) (eV) of ZnTe and its ions
System
Method ΔE IP EA
ZnTe
MP2- LANL2DZ
(2.30)
5.25
2.90
CCSD(T)-LANL2DZ
1.35
4.81
3.46 (3.53)
ZnTe+
UMP2- LANL2DZ
1.23
4.76
3.53
UCCSD(T)-LANL2DZ
1.11
4.73
3.62
ZnTe-
2.58
3.51
0.93
2.63
3.59
0.95
The energitic gap resulted from MP2 is in excellent agreement with the experimental value.
The electron affinity calculated at the CCSD(T) level is in good agrement with the experimental value.
The evolution of ionization potentials and electron affinities follow the orders : IP neutral ˃ IP cation ˃ IP anion
EA cation ˃ EA neutral ˃ EA anion

9. ZnTe Dissociation (0.19 eV) De=1.195 eV De=1.588 eV De=1.143 eV
De(exp)=0.95 eV

10. ZnTe+ Dissociation
De= 0.52 eV
De= 1.08 eV
De= 1.15 eV

11. ZnTe- Dissociation
De= 0.69 eV
De= 0.9 eV
De= 1.01 eV

12. Potential energy surface graphs of ZnTe
The states X1Σ + , a3Π , A1Π converge towards the dissociation limit :
Zn (1S) +Te (1D)
The states c3Π , b3Σ + C1Π converge towards the dissociation limit :
Zn (1S) +Te (3P)
The states d 3Σ + , B1Σ + converge towards the dissociation limit :
Zn (1S) +Te (1S)
Two crosses between the states X1Σ + and a3Π as well as the states c3Π and b3Σ + , due to the rotational interactions of the type
spin -orbite
C. A. Fancher, H. L. de Clercq, O. C. Thomas, D. W. Robinson, and K. H. Bowena J. Chem. Phys., Vol. 109, No. 19, 1998 (Zinc oxide and its anion)

13. Potential energy surface graphs of ZnTe+
The states X2Π , a4Σ + , A2Σ + converge towards the dissociation limit
Zn+ (2S) +Te (3P)
The states c2Π , B2Σ + b4Π converge towards the dissociation limit :
Zn+ (2S) +Te (1D)
The states d 4Σ + , c4Π converge towards the dissociation limit :
Zn+ (2S) +Te (1S)
A Maatouk, A BenHouria, O Yazidi, N Jaidane and M Hochlaf J. Phys. B: At. Mol. Opt. Phys. 44 (2011) ,(Theoretical investigations of the MgO+ cation )

14. Potential energy surface graphs of ZnTe-
The states X2Σ + , A2Π , B2Σ + converge towards the dissociation limit :
Zn (1S) +Te- (2P)
A cross between the states X2Σ + and A2Π + due to the rotational interactions of the type
spin -orbite
C. A. Fancher, H. L. de Clercq, O. C. Thomas, D. W. Robinson, and K. H. Bowena J. Chem. Phys., Vol. 109, No. 19, 1998 (Zinc oxide and its anion)

15. Table 2: Spectroscopic constants of the different states of ZnTe and its ions
System
State
Re / (A°)
ωe /Cm-1
ωeXe/Cm-1
Be/Cm-1
αe/Cm-1
De (eV)
ZnTe
X1Σ +
2.44
1.794
1.12
B1Σ +
1.02
A 1Π
2.6
1.09
C1Π 4
0.95
b 3Σ +
1.69
d 3Σ +
2.8
0.59
a 3Π
2.7
0.29
c 3Π 3
1.34
ZnTe+
X2Π
0.99
C2Π
66.515
0.032
A2Σ +
0.79
B2Σ +
0.21
b4Π
0.62
c4Π 6 -
d4Σ + 8
a4Σ +
ZnTe-
X2Σ +
2.5
2.3
3.24
A2Π
76.794
0.18

16. The previous table reveals the following:
Concerning ZnTe , the same value of Re is observed for X1Σ + and B1Σ +
(R"e = Re' ).
The internuclear distance Re stay invariant during the transition, this is the first case of Franck Condon principle.
The Re value of A 1Π is larger than that of X1Σ + , this is the second case of Franck Condon principle.
The Re value of C 1Π is completely different from that of X1Σ + , this is the third case of Franck Condon principle.
The majority of the vibrational frequencies of the excited states are greater than that of the ground state.

17. We note the absence of potential wells for the states c4Π, d4Σ + and a4Σ + for ZnTe+. These states have very large internuclear distances and tend towards the ionization.
The electronic state of C2Π has a very low dissociation energy.
For ZnTe- , the transition X2Σ + - B2Σ + is placed within the framework of the second case of Franck Condon's principle ( Re' > R"e ).
The electronic state B2Σ + gives the highest dissociation energy although the state A2Π indicates the lowest dissociation energy.

18. Evolution of transition moments
ZnTe
Sudden jumps are noted; This is explained by the existence of the avoided crosses between the curves of potential energy at these particular distances.
These transition dipole moments will be useful in the design of future experiments on the studied system. We recall that zinc and tellurium were detected in the interstellar medium.

19. Excited states properties of ZnTe and its ions
λ= nm
f=1.48
λ= nm
f=0.92
λ= nm
f=0,99
The oscillator strength increases when moving from ZnTe to ZnTe – to ZnTe+
ZnTe- presents wavelengths greater than those of ZnTe and ZnTe

20. First case of Franck Condon's principle
Conclusion 1 2 3
Pour ZnTe, the internuclear distance Re is unchanged during the transition
X2Σ + -A1Π.
First case of Franck Condon's principle
The electronic states of ZnTe converge to the following lower dissociation limits:
Zn (1S) +Te (3P)
Zn (1S) +Te (1D)
Zn (1S) +Te (1S).
The electronic states of ZnTe+ converge to the following lower dissociation limits:
Zn+ (2S) +Te (3P)
Zn+ (2S) +Te (1D)
Zn+ (2S) +Te (1S).

21. (Third case of Franck Condon's principle).
Conclusion 4 5 6
The state C2Π
of ZnTe + is unstable (very low dissociation energy). The internuclear distance of this state is much greater than that of the ground state  
(Third case of Franck Condon's principle).
Crossings between the excited states of ZnTe and ZnTe- are observed. This is due to the presence of rotational and spin-orbit interactions.
The electronic states of ZnTe- converge to the next lowest dissociation limit:
Zn (1S) +Te- (2P).

22. The transitions of ZnTe + require very high energies of excitation
Conclusion 7 8 9
The evolution of transition dipole moments is useful in the design of future experiments (fluorescence, luminescence, etc.) for the ZnTe molecule and its ions
An increase in the oscillator force (f) is observed moving from ZnTe to ZnTe - to ZnTe +.
The transitions of ZnTe + require very high energies of excitation
The electronic state B2Σ + of ZnTe- gives the highest dissociation energy although the state A2Π has the lowest dissociation energy

23. Considering other diatomic and triatomic systems
Perspectives
Considering other diatomic and triatomic systems
Study of Rydberg and valence states.
Radiative lifetimes
More advanced methods: MRCI, F12
Perspectives

24. Thank You for Your Attention
Prof O. OUAMERALI
Dr. N.E. BENSIRADJ :This presentation is one part of the work of her
Doctoral thesis
A. DEKHIRA Ph.D. student.
V. TIMON : Spain, Collaboration.