(He–He) [9, 10] was investigated by coupled cluster calculations. At a local minimum, bonding and anti-bonding molecular orbitals (MOs) were obtained. By the
use of our chemical bonding rule [11, 12], it was concluded that covalent bonding is
formed at optimized structure, due to orbital overlap between helium 1s orbitals.
Bond order is approximate equation to investigate a stability of chemical
bonding in two-atom system:
N =
N a − N b
2
where N a and N b denote the number of electrons in bonding and its anti-bonding
MOs. In the case of helium dimer, bonding and anti-bonding MOs are formed
between helium 1s orbitals. Since two electrons occupy both MOs (N a = N b = 2),
N becomes zero. It was understood that covalent bonding is formed, even if bond
order is zero [10].
In this study, we have investigated chemical bonding character between helium
and hydrogen. The coupled cluster calculations have been performed for He–H
model. Here, three different hydrogen formal charges have been assumed: (1) positive (H
+
); (2) neutral (H); (3) negative (H
−
).
2 Computations
2.1 Calculation Method and Model
The calculations presented here were performed using the coupled cluster singles
and doubles (CCSD) method. It is because CCSD method accurately reproduces
accurate interatomic distance, electronic state and molecular spectra for simple
molecule [13, 14]. We used aug-cc-pVTZ basis set for helium and hydrogen [15].
All calculations were performed with the Gaussian program [16]. To investigate
chemical bonding character between helium and hydrogen, the simple He–H model
was constructed. Three types of He–H
+ , He–H and He–H
− models were constructed.
Potential energy curves were obtained, changing the interatomic distance. In addition, zero point vibrational energy has been also obtained at the optimized structure.
2.2 Chemical Bonding Rule
In order to judge chemical bonding character such as covalency and ionicity in the
calculated MOs, chemical bonding rule is very useful and applicable (see Fig. 1).
How to utilize chemical bonding rule
1. In MOs including outer shell electrons, check whether the orbital overlap
between helium and hydrogen exists or not.
204
T. Onishi
use of our chemical bonding rule [11, 12], it was concluded that covalent bonding is
formed at optimized structure, due to orbital overlap between helium 1s orbitals.
Bond order is approximate equation to investigate a stability of chemical
bonding in two-atom system:
N =
N a − N b
2
where N a and N b denote the number of electrons in bonding and its anti-bonding
MOs. In the case of helium dimer, bonding and anti-bonding MOs are formed
between helium 1s orbitals. Since two electrons occupy both MOs (N a = N b = 2),
N becomes zero. It was understood that covalent bonding is formed, even if bond
order is zero [10].
In this study, we have investigated chemical bonding character between helium
and hydrogen. The coupled cluster calculations have been performed for He–H
model. Here, three different hydrogen formal charges have been assumed: (1) positive (H
+
); (2) neutral (H); (3) negative (H
−
).
2 Computations
2.1 Calculation Method and Model
The calculations presented here were performed using the coupled cluster singles
and doubles (CCSD) method. It is because CCSD method accurately reproduces
accurate interatomic distance, electronic state and molecular spectra for simple
molecule [13, 14]. We used aug-cc-pVTZ basis set for helium and hydrogen [15].
All calculations were performed with the Gaussian program [16]. To investigate
chemical bonding character between helium and hydrogen, the simple He–H model
was constructed. Three types of He–H
+ , He–H and He–H
− models were constructed.
Potential energy curves were obtained, changing the interatomic distance. In addition, zero point vibrational energy has been also obtained at the optimized structure.
2.2 Chemical Bonding Rule
In order to judge chemical bonding character such as covalency and ionicity in the
calculated MOs, chemical bonding rule is very useful and applicable (see Fig. 1).
How to utilize chemical bonding rule
1. In MOs including outer shell electrons, check whether the orbital overlap
between helium and hydrogen exists or not.
204
T. Onishi