Ab-Initio Geometry Optimization of Large Molecules

描述(申请人提供)：虽然密度泛函能量计算现在对生物分子是可行的，但密度泛函几何优化器的使用仍然局限于包含不超过30个原子的相对较小的分子。传统的密度泛函几何优化器的主要局限性是，几何优化的成本至少与分子中的原子数量成二次曲线关系。相反，固定几何构型下的能量可以根据与分子大小成线性比例的成本进行评估，从而使非常大的分子能够被处理。这一建议是基于对密度泛函几何优化算法的根本改变，潜在地将分子大小的总成本从二次型降低到线性，并使可优化的分子大小实现了量子飞跃。该算法类似于传统的在固定几何结构下的能量自洽计算，但在收敛时，该算法不仅可以得到密度，还可以得到优化的几何形状。这是通过通过修改的自洽场过程同时优化波函数和几何来实现的。建议的算法将在QChem软件包中实现，如果成功，将通过QChem Inc.和Spartan Inc.广泛分发。

DESCRIPTION (provided by applicant): While density-functional calculations of the energy are now feasible for biomolecules, the use of density-functional geometry optimizers is still confined to relatively small molecules containing no more than thirty atoms. The key limitation of conventional density-functional geometry optimizers is that the cost of the geometry optimization scales at least quadratically with the number of atoms in the molecule. In contrast the energy at a fixed geometry can be evaluated for a cost which scales linearly with molecule size, enabling very large molecules to be treated. This proposal is based on a radical change in the algorithm for density-functional geometry optimization, potentially reducing the total cost from quadratic to linear in molecule size and enabling a quantum leap in the size of molecules that can be optimized. The proposed algorithm resembles a conventional self-consistent calculation of the energy at a fixed geometry but at convergence the proposed algorithm yields not only the density but also the optimized geometry. This is achieved by simultaneous optimization of the wavefunction and the geometry via a modified self-consistent-field procedure. The proposed algorithm will be implemented in the QChem software package and, if successful, widely distributed through QChem Inc. and Spartan Inc.