Abstract
Potential energy surface scanning for UC, UN, and UH was performed by configuration interaction (CI), coupled cluster singles and doubles (CCSD) excitation, quadratic configuration interaction (QCISD (T)), and density functional theory PBE1 (DFT-PBE1) methods in coupling with the ECP80MWB_AVQZ + 2f basis set for uranium and 6 − 311 + G∗for carbon, hydrogen, and nitrogen. The dissociation energies of UC, UN, and UH are 5.7960, 4.5077, and 2.6999 eV at the QCISD (T) levels, respectively. The calculated energy was fitted to the potential functions of Morse, Lennard-Jones, and Rydberg by using the least square method. The anharmonicity constant of UC is 0.0047160. The anharmonic frequency of UC is 780.27 cm−1which was obtained based on the PBE1 results. For UN, the anharmonicity constant is 0.0049827. The anharmonic frequency is 812.65 cm−1which was obtained through the PBE1 results. For UH, the anharmonicity constant is 0.017300. The anharmonic frequency obtained via the QCISD (T) results is 1449.8 cm−1. The heat capacity and entropy in different temperatures were calculated using anharmonic frequencies. These properties are in good accordance with the direct DFT-UPBE1 results (for UC and UN) and QCISD (T) results (for UH). The relationship of entropy with temperature was established.
Highlights
Among various theoretical simulation methods for molecules and materials, the first principles and molecular dynamic simulation techniques are very powerful for computing the micro and macro properties [1, 2]. e properties and phenomena in materials typically occur at multiple time and length scales. erefore, to investigate the dynamic behaviors and the time evolution processes, one should resort to the molecular dynamics simulations instead of the first principles [3]
It is computationally too expensive or impractical to use methods such as CASSCF to establish the potential energy surface of UC, UN, and UH. en, we selected the less expensive ab initio configuration interaction (CI), coupled cluster singles and doubles (CCSD), QCISD (T), and DFT-PBE1 methods to determine the potential energy surface. e calculations described in this paper were performed with the Gaussian 09 package [14]. e DFT method is at the PBE1 level. e basis sets for uranium is ECP80MWB_AVQZ + 2f and 6 − 311 + G∗ for carbon, nitrogen, and hydrogen [15]
Potential Energy. e potential energy surfaces of UC, UN, and UH were obtained by the CCSD, CI, QCISD (T), and DFT-PBE1 methods
Summary
Among various theoretical simulation methods for molecules and materials, the first principles and molecular dynamic simulation techniques are very powerful for computing the micro and macro properties [1, 2]. e properties and phenomena in materials typically occur at multiple time and length scales. erefore, to investigate the dynamic behaviors and the time evolution processes, one should resort to the molecular dynamics simulations instead of the first principles [3]. Among various theoretical simulation methods for molecules and materials, the first principles and molecular dynamic simulation techniques are very powerful for computing the micro and macro properties [1, 2]. Erefore, to investigate the dynamic behaviors and the time evolution processes, one should resort to the molecular dynamics simulations instead of the first principles [3]. Molecular dynamics simulation with a molecular force field is a practical method to calculate the dynamic property of the condensed materials [4]. The potential function is necessary for establishing and optimizing the force field parameters, which in turn plays an important role for investigating static and dynamic properties of molecules as well as of solid states [10, 11]
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