Geometry optimization of large molecules with quantum Monte Carlo

先进的计算工具的可用性，以准确和有效地描述复杂系统中的光诱导过程是开发人工光合作用，光催化，生物成像和光医学应用新技术的关键。然而，计算激发态对电子结构方法的要求很高，这些方法通常难以确保准确性或处理大型相关系统尺寸。为了克服这些限制，我们将在量子蒙特卡罗方法的替代框架中工作，该框架使用随机算法来求解Schrödinger方程，很好地适应系统大小，并提供对基态和电子激发态的平衡描述。在这里，我们打算进一步推动这种方法，并将其应用于计算基态和激发态大分子系统的结构性质。为此，我们将通过开发具有小波动和减少偏差特征的改进估计器，加速确定最佳结构和反应途径所需的原子间力的计算。这将允许相当短的蒙特卡罗模拟和同样精确的结构与使用更简单的波函数，因此，开放的可能性，以处理更大的系统。此外，我们计划扩展和探索更精确和鲁棒的扩散蒙特卡罗方法在结构松弛中的应用。通过这些发展所取得的进展将在施坦豪斯加合分子的光诱导开关机制的研究中得到证明，这是一种新型的合成光开关，在材料科学和生物系统中具有广阔的应用前景。

The availability of advanced computational tools to accurately and efficiently describe light-induced processes in complex systems is key to the development of new technologies for artificial photosynthesis, photo-catalysis, bio-imaging, and photo-medical applications. Computing excited states, however, is highly demanding for electronic structure methods, which often struggle to ensure accuracy or to treat the large, relevant system sizes. To overcome these limitations, we will work in the alternative framework of quantum Monte Carlo methods which use stochastic algorithms to solve the Schrödinger equation, scale well with system size, and offer a balanced description of the ground and electronic excited states. Here, we intend to further push this methodology and extend its applicability to the computation of structural properties of large molecular systems in the ground and excite states. To this aim, we will accelerate the computation of interatomic forces required to determine optimal structures and reaction pathways, by developing improved estimators characterized by small fluctuations and reduced bias. This will allow for considerably shorter Monte Carlo simulations and equally accurate structures with the use of simpler wave functions and, therefore, open the possibility to treat significantly larger systems. Furthermore, we plan to extend and explore the use of the more accurate and robust diffusion Monte Carlo method to structural relaxation. The advances achieved via these developments will be demonstrated on the study of the photoinduced switching mechanism of donor-acceptor Stenhouse adduct molecules, a novel class of synthetic photoswitches with promising applications in material science and biological systems.