The other main type of atomistic simulations, electronic structure methods, employ a much more detailed physical description of how atoms interact, specifically via the electrons, based on quantum mechanics. These methods can further be divided into two categories: ab initio or first-principles methods (where density functional theory, DFT, is the most widely used in materials science), and semi-empirical models.
As the name implies, first-principles methods do not require any a prior knowledge of the interactions between the atoms. In essence, the only necessary input for these calculations are the positions of all the atoms in the system, a model for how atoms generally interact (which usually involves certain numerical approximations to reduce the calculation time), and an electronic description of each chemical element. Semi-empirical methods are also quantum-mechanical, but less general, since they (akin to force fields) use predefined parameters for some terms in the interactions between atoms.
First-principles methods can be used for the same studies as force fields, but with a much broader application range, as atoms of different elements can be combined in all possible, arbitrary ways, without a need to adjust any parameters for each case. In practice, however, the simulations are limited to much smaller systems, typically below 10,000 atoms, due to increased computational complexity of the governing equations. Semi-empirical electronic structure methods can handle larger systems, even up to millions of atoms, but are often hard to parametrize for systems with many different chemical elements, and each parameter set is usually only valid for a particular type of material.
Electronic structure methods allow for studying a large number of material properties, including electrical properties such as resistivity and mobility, and whether a material is a metal, semiconductor, or an insulator, by estimating the band gap. Optical and magnetic properties can also be obtained, and one can investigate effects that derive purely from quantum mechanics, such as superconductivity, topological invariants, tunnelling, and many others. Additionally, it is equally possible to perform ab initio MD (AIMD) simulations to obtain thermal and mechanical properties, but these are generally very time-consuming calculations.