月別: 2022年2月

[Published online Journal of Computer Chemistry, Japan Vol.20, 126-128, by J-STAGE]
<Title:> 虚数時間発展法による電子状態計算手法の開発
<Author(s):> 王　欽林, 善甫　康成
<Corresponding author E-Mill:> qinlin.wang.3p(at)stu.hosei.ac.jp
<Abstract:> We have been studying the time-evolution technique in imaginary time. The electronic structure calculated in this technique is valid for the ground state, which is easily confirmed from the completeness of the wavefunction. However, the excited states can be also obtained by Gram-Schmidt orthogonalization technique. As a practical 3D calculation, we applied this technique to hydrogen atom and molecule systems. The results are in good agreement with their analytical solutions, including the excited states. The purpose of this study is to present the effectiveness of this technique for practical electronic structure calculations. To realize it, we will start to apply this to hydrogen and practical small molecule systems.
<Keywords:> Time-evolution technique, Imaginary time, Electronic structure calculation
<URL:> https://www.jstage.jst.go.jp/article/jccj/20/3/20_2021-0032/_article/-char/ja/

[Published online Journal of Computer Chemistry, Japan -International Edition Vol.8, -, by J-STAGE]
<Title:> Analyses of Optical Gains and Oscillation Wavelengths for Quantum Cascade Lasers Using the Nonequilibrium Green’s Function Method
<Author(s):> Hirotaka TANIMURA, Shigeyuki TAKAGI, Tsutomu KAKUNO, Rei HASHIMOTO, Kei KANEKO, Shinji SAITO
<Corresponding author E-Mill:> takagisgyk(at)stf.teu.ac.jp
<Abstract:> We have succeeded in improving the gain of the base quantum cascade laser (QCL) through experiments and device simulations using the nonequilibrium Green’s function (NEGF) method, and we investigate the factor that increases the gain by reducing the thickness of the barrier by 10%. Specifically, we analyzed the minibands (Wannier Stark states), density of states (DOS), and electron density that contribute to the emission. The results show that the gain enhancement is due to the increase in the electron density of the quantum wells in the active region and the increase in the oscillator strength between the minibands that contribute to the emission. Quantum mechanical calculation like the NEGF method is very effective for mesoscopic systems such as the active layer of QCL.
<Keywords:> Nonequilibrium Green’s function, Quantum cascade laser, Optical gain, Electroluminescence, Current voltage characteristic, Oscillation wavelength, Density of states, Electron density, Oscillator strength
<URL:> https://www.jstage.jst.go.jp/article/jccjie/8/0/8_2021-0024/_html