Neufeld Ofer, Nourbakhsh Zahra, Tancogne-Dejean Nicolas, Rubio Angel
Max Planck Institute for the Structure and Dynamics of Matter and Center for Free-Electron Laser Science, Hamburg 22761, Germany.
Center for Computational Quantum Physics (CCQ), The Flatiron Institute, New York, New York 10010, United States.
J Chem Theory Comput. 2022 Jul 12;18(7):4117-4126. doi: 10.1021/acs.jctc.2c00235. Epub 2022 Jun 14.
High harmonic generation (HHG) takes place in all phases of matter. In gaseous atomic and molecular media, it has been extensively studied and is very well understood. In solids, research is ongoing, but a consensus is forming for the dominant microscopic HHG mechanisms. In liquids, on the other hand, no established theory yet exists, and approaches developed for gases and solids are generally inapplicable, hindering our current understanding. We develop here a powerful and reliable ab initio cluster-based approach for describing the nonlinear interactions between isotropic bulk liquids and intense laser pulses. The scheme is based on time-dependent density functional theory and utilizes several approximations that make it feasible yet accurate in realistic systems. We demonstrate our approach with HHG calculations in water, ammonia, and methane liquids and compare the characteristic response of polar and nonpolar liquids. We identify unique features in the HHG spectra of liquid methane that could be utilized for ultrafast spectroscopy of its chemical and physical properties, including a structural minimum at 15-17 eV that is associated solely with the liquid phase. Our results pave the way to accessible calculations of HHG in liquids and illustrate the unique nonlinear nature of liquid systems.
高次谐波产生（HHG）在物质的所有相中都会发生。在气态原子和分子介质中，它已得到广泛研究且被很好地理解。在固体中，研究仍在进行，但对于主要的微观HHG机制正在形成共识。另一方面，在液体中，尚未存在既定的理论，并且为气体和固体开发的方法通常不适用，这阻碍了我们目前的理解。我们在此开发了一种强大且可靠的基于从头算团簇的方法，用于描述各向同性体液体与强激光脉冲之间的非线性相互作用。该方案基于含时密度泛函理论，并利用了几种近似方法，使其在实际系统中既可行又准确。我们通过对水、氨和甲烷液体的HHG计算来展示我们的方法，并比较极性和非极性液体的特征响应。我们确定了液态甲烷HHG光谱中的独特特征，这些特征可用于其化学和物理性质的超快光谱研究，包括在15 - 17 eV处的一个结构最小值，该最小值仅与液相相关。我们的结果为液体中HHG的可及计算铺平了道路，并说明了液体系统独特的非线性性质。
