The suboption VELOCITIES will result in a restart from both, ionic and wavefunction velocities. In special cases, this is not the desired behavior. Using the additional keyword QUENCH the read velocities can be set back to zero. This will be most likely used for wavefunctions with QUENCH ELECTRONS. Another possibility is to reoptimize the wavefunction at the start of a molecular dynamics simulation. This is achieved with the keywords QUENCH BO. Note: this does not set the wavefunction velocities to zero, you have to add the ELECTRONS option to do this. This is probably the reasonable choice, because the requirement to quench the wavefunction to the BO-surface usually stems from the fictitious degrees of freedom picking up too much kinetic energy.
For performance reasons the writing of the restart http should be done only occasionally particularly when running large systems and the storage area is on a networked httpsystem. This might cause problems if the simulation was terminated incorrectly. Several hundreds or thousands of simulation steps might be lost. For this reason CPMD writes a special output http GEOMETRY after each molecular dynamics step. Together with a normal restart http this allows to start the simulation form the last ionic configuration and velocities. To achieve this another suboption GEOFILE has to be added to the RESTART keyword. After reading the positions and velocities of the ions from the restart http, they are also read and overwritten from the GEOMETRY http and overwritten.
Special restarts to be used with the keywords TDDFT and VIBRATIONAL ANALYSIS are discussed in the sections covering that type of simulations.