Slides

Ab initio MD: CPMD
• Therefore the MD methods introduces a limita4on with respect to the choice of the
maximum 4me step that can be used, which is inversely propor4onal to the highest
frequency in the system:
Δt max ∝ 1
ω e
max ∝ µ
E cut
• Thus, a too small electronic mass entails very small 4me steps, therefore one has to find
a compromise on the control parameter μ:
• Typical values: μ = 500-­‐1000 a.u allowing for a 4me step of
0.12 – 0.24 fs depending on the mass of the lightest nuclei.
• μ too small: 4me steps too small
• μ too large: adiaba4city lost
• Replacing hydrogen by deuterium allows for a large 4me step and s4ll increase μ.
• Thermostat electronic mo4on independently from nuclei.