There are molecular mechanics/molecular dynamics methods that use only classical physics ("ball and spring" models). That's part of computational chemistry.
To elaborate on your comments, most of computational chemistry does use quantum mechanical models, and there are indeed difficult problems with computational intensity. Basic quantum chemical methods start with a big-O time complexity of O(N^4). The "gold standard" of computational chemistry, CCSD(T), is O(N^7). It is the worst-scaling method that still sees routine use.
An "exact" [1] approach to electronic structure calculations, full configuration interaction, scales as O(N!) -- yes, factorial. Not surprisingly, the size of systems tractable via FCI has not grown much in 30 years even as computers have grown much faster.
There is indeed a lot of work applied developing efficient approximations to the "exact" quantum mechanical solution, and to eking out more constant-factor improvements from existing algorithms.
There's also a lot of work on taking electronic structures, available from various methods, and deriving familiar chemical properties from them. Things like NMR spectra, Raman spectra, pKa, melting point, aqueous solubility...
Measuring properties of bulk condensed-phase matter in the lab is easy but it's hard in simulation. Something "basic" like melting point is very hard to derive from ab initio calculations. On the other hand, properties that require expensive equipment to measure, like NMR spectra, are comparatively easy to calculate.
[1] Terms and conditions apply. Consult Helgaker et al. "Molecular Electronic‐Structure Theory" for details.
To elaborate on your comments, most of computational chemistry does use quantum mechanical models, and there are indeed difficult problems with computational intensity. Basic quantum chemical methods start with a big-O time complexity of O(N^4). The "gold standard" of computational chemistry, CCSD(T), is O(N^7). It is the worst-scaling method that still sees routine use.
https://en.wikipedia.org/wiki/Ab_initio_quantum_chemistry_me...
An "exact" [1] approach to electronic structure calculations, full configuration interaction, scales as O(N!) -- yes, factorial. Not surprisingly, the size of systems tractable via FCI has not grown much in 30 years even as computers have grown much faster.
There is indeed a lot of work applied developing efficient approximations to the "exact" quantum mechanical solution, and to eking out more constant-factor improvements from existing algorithms.
There's also a lot of work on taking electronic structures, available from various methods, and deriving familiar chemical properties from them. Things like NMR spectra, Raman spectra, pKa, melting point, aqueous solubility...
Measuring properties of bulk condensed-phase matter in the lab is easy but it's hard in simulation. Something "basic" like melting point is very hard to derive from ab initio calculations. On the other hand, properties that require expensive equipment to measure, like NMR spectra, are comparatively easy to calculate.
[1] Terms and conditions apply. Consult Helgaker et al. "Molecular Electronic‐Structure Theory" for details.