**Author details**

is [Omim]TFO, which indicates that [Omim]BF4 and [Omim]TFO have strong ability to attract electrons. The global hardness (*η*) of [Omim]BF4 and [Omim]TFO is larger, the global softness (*S*) is smaller and the electrophilic index (*ω*) is larger, which indicates that [Omim]BF4 and [Omim]TFO are ionic liquids with better corrosion inhibition performance. For the polarizability (*α*), [Omim]TFO is the largest, which indicates that [Omim]TFO is the most easily adsorbed on the iron surface, and its corrosion inhibition effect is the best. In conclusion, [Omim]TFO has the best corrosion inhibition performance and the highest efficiency among the

The reaction activities such as *E*LUMO, *E*HOMO, the softness (*S*) and polarizability (*α*) increase gradually, whereas electronegativity (*χ*), energy gap (Δ*E*), hardness (*η*), dipole moment (*μ*) and electrophilic index (*ω*) of three sets ionic liquids 1 alkyl-3-methylimidazole chloride [Cnmim]Cl, 1-alkyl-3-methylimidazolium acetate [Cnmim]Ac and 1-octyl-3-methylimidazole salt [Omim]Y were studied by density

In [Cnmim]Cl and [Cnmim]Ac system, increasing the length of the alkyl chain, the HOMO energy *E*HOMO, LUMO energy ELUMO, softness (*S*) increase, while the dipole moment (*μ*), energy gap Δ*E*, electronegativity (*χ*), electrophilic index (*ω*), hardness (*η*) and polarizability (*α*) gradually decrease. In [Omim]Y (Y = Cl, BF4, HSO4, Ac, TFO) ionic liquids, the structure parameters of ionic liquids vary greatly

The active region of [Cnmim]Cl system is the imidazole ring and anion Cl, while the [Cnmim]Ac system is located in the imidazole ring and the O atoms of anion. The active region of [Omim]Y system is located in the imidazole ring and an oxygen-containing group. The reaction is the active region of ionic liquid molecules will help interact with the iron surface and stably adsorb on the iron surface.

For [Cnmim]Cl system, the order of inhibition efficiency predicted is [C8mim] Cl > [C6mim]Cl > [C4mim]Cl > [C2mim]Cl, and [Omim]Cl may have the best inhibition effect. For [Cnmim]Ac system, the order of inhibition efficiency is [C8mim]Ac > [C6mim]Ac > [C4mim]Ac > [C2mim]Ac, and [Omim]Ac may have the best inhibition effect. Inhibition efficiency increases by increasing the alkyl chain length. For [Omim]Y system, [Omim]TFO may have better inhibition effi-

This work was supported in part by the National Natural Science Foundation of China (51774158, 5126402) and Back-up Personnel Foundation of Academic and

ciency, and the sequence of inhibition efficiency needs further study.

Technology Leaders of Yunnan Province (2011HR013).

The authors declare no conflict of interest.

11 ionic liquids studied.

*Density Functional Theory Calculations*

with different anions.

**Acknowledgements**

**Conflict of interest**

**50**

functional theory. The results are as follows:

**4. Conclusion**

Guocai Tian\* and Weizhong Zhou State Key Laboratory of Complex Nonferrous Metal Resource Clean Utilization, Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Yunnan, Kunming, China

\*Address all correspondence to: tiangc@kust.edu.cn

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