Theoretical investigation of pressure-induced structural transitions in americium using GGA + U and hybrid density functional theory methods

Ashok K. Verma; P. Modak; SurinderM. Sharma; A. Svane; N. E. Christensen; S. K. Sikka

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Theoretical investigation of pressure-induced structural transitions in americium using GGA + U and hybrid density functional theory methods

机译：利用GGA + U和混合密度泛函理论方法对methods中压力诱导的结构转变的理论研究

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First-principles calculations have been performed for americium (Am) metal using the generalized gradient approximation + orbital-dependent onsite Coulomb repulsion via Hubbard interaction (GGA + U) and hybrid density functional theory (HYB-DFT) methods to investigate various ground state properties and pressure-induced structural transitions. Both methods yield equilibrium volume and bulk modulus in good agreement with the experimental results. The GGA + spin orbit coupling + U method reproduced all structural transitions under pressure correctly, but the HYB-DFT method failed to reproduce the observed Am-Ⅰ to Am-Ⅱ transition. Good agreement was found between calculated and experimental equations of states for all phases, but the first three phases need larger U (α) parameters (where α represents the fraction of Hartree-Fock exchange energy replacing the DFT exchange energy) than the fourth phase in order to match the experimental data. Thus, neither the GGA + U nor the HYB-DFT methods are able to describe the energetics of Am metal properly in the entire pressure range from 0 GPa to 50 GPa with a single choice of their respective U and α parameters. Low binding-energy peaks in the experimental photoemission spectrum at ambient pressure relate, for some parameter choices, well to peak positions in the calculated density of states function of Am-Ⅰ.

机译：Hub（Am）金属的第一性原理已通过Hubbard相互作用（GGA + U）和混合密度泛函理论（HYB-DFT）方法使用广义梯度近似+轨道相关的现场库仑排斥力进行了研究，以研究各种基态性质和压力引起的结构转变。两种方法均产生平衡体积和体积模量，与实验结果吻合良好。 GGA +自旋轨道耦合+ U方法正确地再现了在压力下的所有结构转变，但HYB-DFT方法未能再现观察到的Am-Ⅰ至Am-Ⅱ转变。在所有阶段的计算状态方程和实验状态方程之间都发现了很好的一致性，但是前三个阶段比第四个阶段需要更大的U（α）参数（其中α表示Hartree-Fock交换能的分数代替DFT交换能）。为了匹配实验数据。因此，GGA + U和HYB-DFT方法都无法通过选择各自的U和α参数来正确描述Am金属在0 GPa至50 GPa整个压力范围内的能级。对于某些参数选择，在环境压力下，实验光发射光谱中的低结合能峰与计算出的Am-Ⅰ态密度函数中的峰位置有关。

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《Physical review》 |2013年第1期|014111.1-014111.7|共7页
作者
Ashok K. Verma; P. Modak; SurinderM. Sharma; A. Svane; N. E. Christensen; S. K. Sikka;
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作者单位

High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India;

High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India;

High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India;

Department of Physics and Astronomy, University of Aarhus, DK 8000, Aarhus C, Denmark;

Department of Physics and Astronomy, University of Aarhus, DK 8000, Aarhus C, Denmark;

Office of the Principal Scientific Adviser to Government of India, Vigyan Bhawan Annexe, Maulana Azad Road, New Delhi 110011, India;

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density functional theory, local density approximation, gradient and other corrections; pressure effects;

机译：密度泛函理论;局部密度近似;梯度和其他校正;压力效应;

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Theoretical investigation of pressure-induced structural transitions in americium using GGA + U and hybrid density functional theory methods

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