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what are multi scale methods?
When small scale and large scale calculations are run simultaneously
what are continuum methods?
only dielectric medium, no atoms
what is a force field?
Sum of intramolecular and intermolecular interactions
what is the born oppenheimer assumption?
Electrons move faster than nuclei so the nuclei can be considered as stationary and the electrons are moving in the constant potential energy field.
explain the molecular mechanic explanation why eletcron electron interactions can be ignored?
electrons move so fast that we only see an average distribution of electrons around a nucleus. If we are only interested in nuclei positions we can consider only nuclei - nuclei interactions.
`give the equation for hookes law?
E = 0.5K (X - Xo)^2
what is storic energy?
The amount of strain in a molecules bond length
what is the equation for force relating to hookes law?
F = -K (x-xo)
what happens is x= xo x>xo x < xo
when x and xo are = the atoms are in ideal positions when x is greater than xo then F<0 and pushes atoms to left . when x is less than xo then F > 0 and force drives atom to right
what are the advantages of quantum mechanics?
Rigorous description of ee and e nuclei interactions Abinito- no experimental input can cope with new structures only method for electronic properties
disadvantages of quantum mechanics?
slow to solve Schrodinger equation needs high accuracy of qm
disadvantages of quantum mechanics?
slow to solve Schrodinger equation needs high accuracy of qm
advantages of molecular mechanics?
v fast allows dynamics of molecules to be studied applicable to large systems if properly paramertised then can be as accurate as QM
what are the disadvantages of molecular mechanics?
parameters need to be chosen cant cope with new structures QM of experiment needs to be done first applicable to describing molecules not electronic properties
when to use quantum mechanics?
for electronic properties MO, excited states, light absorptions, bond rearrangement and charge transfer
when to use to molecular mechanics?
large systems, large molecules (Bimolecular), dymanics of molecules, molecules in solution, organic inorganic interfaces and metal organic molecules.
what the three bending terms?
Stretch, bending and torsional
what is the equation for steric energy?
E = Estretch + Ebend + Etorsion
name the three out of plane terms?
Non planar molecules Cross terms - bond deformations affect electron distribution stretch bend vibrations - these are usually small so not used in force fields
give all the oxygen atom types
O alcohol, O ether, O in C=O in cooh , C-O in COOh
give all the nitrogen atom types
N sp3 - Nh3 or NHR2 N sp2 - 2 atoms bonded N sp3 - 1 atom bonded
give all the sulphur atom types
-s- sulfide s=o sulfoxide si - silane s+ - sulfonium So2 - sulfone
what is the overall equation for Einter interactions?
Eelec + Evdv + Eh-bond
at large distances dipole dipole interactions can be ignored, why?
1/R3 falls to zero more faster than 1/R