V

Name VDW_TS_cutoff
Section Hamiltonian::XC
Type float
Default 10.0

Set the value of the cutoff (unit of length) for the VDW correction in periodic system in the Tkatchenko and Scheffler (vdw_ts) scheme only.

Name VDW_TS_damping
Section Hamiltonian::XC
Type float
Default 20.0

Set the value of the damping function (in unit of 1/length) steepness for the VDW correction in the Tkatchenko-Scheffler scheme. See Equation (12) of Phys. Rev. Lett. 102 073005 (2009).

Name VDW_TS_sr
Section Hamiltonian::XC
Type float
Default 0.94

Set the value of the sr parameter in the damping function of the VDW correction in the Tkatchenko-Scheffler scheme. See Equation (12) of Phys. Rev. Lett. 102 073005 (2009). This parameter depends on the xc functional used. The default value is 0.94, which holds for PBE. For PBE0, a value of 0.96 should be used.

Name VDWCorrection
Section Hamiltonian::XC
Type integer
Default no

(Experimental) This variable selects which van der Waals correction to apply to the correlation functional.

Options:

• none:
  No correction is applied.
  
• vdw_ts:
  The scheme of Tkatchenko and Scheffler, Phys. Rev. Lett. 102 073005 (2009).
  
• vdw_d3:
  The DFT-D3 scheme of S. Grimme, J. Antony, S. Ehrlich, and S. Krieg, J. Chem. Phys. 132, 154104 (2010).
  

Name VDWD3Functional
Section Hamiltonian::XC
Type string

(Experimental) You can use this variable to override the parametrization used by the DFT-D3 van deer Waals correction. Normally you need not set this variable, as the proper value will be selected by Octopus (if available).

This variable takes a string value, the valid values can be found in the source file ’external_libs/dftd3/core.f90’. For example you can use:

VDWD3Functional = ‘pbe’

Name vdWNPoints
Section Linear Response::Polarizabilities
Type integer
Default 6

How many points to use in the Gauss-Legendre integration to obtain the van der Waals coefficients.

Name VDWSelfConsistent
Section Hamiltonian::XC
Type logical
Default yes

This variable controls whether the VDW correction is applied self-consistently, the default, or just as a correction to the total energy. This option only works with vdw_ts.

Name Velocities
Section System::Velocities
Type block

If XYZVelocities, PDBVelocities, and XSFVelocities are not present, Octopus will try to fetch the initial atomic velocities from this block. If this block is not present, Octopus will set the initial velocities to zero. The format of this block can be illustrated by this example:

%Velocities
  ‘C’ | -1.7 | 0.0 | 0.0
  ‘O’ |  1.7 | 0.0 | 0.0
%

It describes one carbon and one oxygen moving at the relative velocity of 3.4 velocity units.

Note: It is important for the velocities to maintain the ordering in which the atoms were defined in the coordinates specifications.

Name VibrationalSpectrumTime
Section Utilities::oct-vibrational_spectrum
Type integer

This variable controls the maximum time for the calculation of the velocity autocorrelation function. The default is the total propagation time.

Name VibrationalSpectrumTimeStepFactor
Section Utilities::oct-vibrational_spectrum
Type integer
Default 10

In the calculation of the vibrational spectrum, it is not necessary to read the velocity at every time step. This variable controls the integer factor between the simulation time step and the time step used to calculate the vibrational spectrum.

Name Volume
Section Utilities::
Type block

Describes a volume in space defined through the addition and substraction of spheres. The first field is always "+" (include points inside the volume) or "-" (exclude points inside the volume)

Options:

• vol_sphere:
  %Volume
     "+"/"-" | vol_sphere | center_x | center_y | center_z | radius
  %
  
• vol_slab:
  %Volume
     "+"/"-" | vol_slab | thickness
  %