Implement basic thermochemistry contributions

[schneiderfelipe]

The following is a brief, cascading outline of all contributions to thermochemistry:

• [x] G = H - T * S
  • [x] H = U + kB * T
  • [x] U = E(el) + E(ZPE) + E(vib) + E(rot) + E(trans)
  • [x] S = S(el) + S(vib) + S(rot) + S(trans)

Above I use the following definitions:

• [x] E(el) is the total electronic energy [equals E(kin-el) + E(nuc-el) + E(el-el) + E(nuc-nuc)]
• [x] S(el) is the electronic entropy
• [x] E(ZPE) is the zero temperature vibrational energy
• [x] E(vib) is the finite temperature correction to E(ZPE) due to populated excited vibrational states
• [x] S(vib) is the vibrational entropy
• [x] E(rot) is the rotational thermal energy
• [x] S(rot) is the rotational entropy
• [x] E(trans) is the translational thermal energy
• [x] S(trans) is the translational entropy

All values incorporated into G, H, and S will be calculated using the following models:

• [x] RRHO
• [x] QRRHO

For some information on how RRHO is implemented in some codes, see here, here and here. All this should be organized in a proper module. Ideas for names: thermo, thermostat, mechstat, rovib, rovibs.

Collateral features

This scheme will allow us to

• [x] calculate all values above for any temperature
• [ ] calculate all values above for any isotope substitution

[schneiderfelipe]

Discussions about kinetic isotope effects were moved to milestone 1.1.

[schneiderfelipe]

Discussions about kinetic isotope effects were moved to milestone 1.1.

This is not related to kinetic isotope effects, so keep it in 1.0.

[schneiderfelipe]

Discussions about kinetic isotope effects were moved to milestone 1.1.

I'll close this despite the points on kinetic isotope effects, which is not the priority right now. Issues #10 and #24 currently deal with the challenges of automatically calculating and simulating for any isotope substitution.