Variables

This page gives a brief explanation of the format and meaning for input variables used by Yambo. Eventually it will be split into separate pages per runlevel, with the Units/Formats appearing just on the main page. Links can be made to runlevel sections with Variables#Initialization and to single variables with Variables#MaxGvecs, etc. Use the template var3. Some characters will mess up the template, such as equal signs - this may explain why some of your text is missing.

Units

• None = no unit
• RL = number of G-vectors
• Energy = Ha, mHa (Hartree atomic units), Ry, mRy (Rydberg atomic units), eV, meV (electron volts), K, THz, GHz
• Length = Bohr atomic units a.u.

Formats

• Integer = integer value
• Real = real value
• Complex = ( real part , imag part )
• String = string
• Range = Lower limit | Upper limit |(in the specified Unit or integer values)
• Scissors = Shift | CB stretch | VB stretch | (Energy | Real | Real)
• Vector = x | y | z | (in Cartesian coordinates, sandwiched by %)

Ranges can also be split on multiple lines.

Initialization

MaxGvecs (Units: RL/Energy, Format: Integer/Real)

Meaning: Number of G-vectors in screening

Tip: This determines the size of the dielectric matrix in G-space. Needed for inclusion of local field effects. It should be much smaller than the number of G-vectors needed to expand the wavefunctions. It needs careful convergence.

Optics-basic

Chimod (Units: None, Format: String)

Meaning: Type of kernel in TDDFT Dyson equation.

Tip: Do not set this manually - set using the appropriate -k command line option. Allowed values: IP/Hartree/ALDA/LRC/BSfxc. IP indicates no kernel (independent particle level/RPA without local fields).

NGBlkXd (Units: RL/Energy, Format: Integer/Real)

Meaning: Number of G-vectors or energy cut off in the screening.

Tip: Determines the size of the dielectric matrix in G-space. Needed for inclusion of local field effects. It should be much smaller than the number of G-vectors needed to expand the wavefunctions. It needs careful convergence.

QpntsRXd (Units: None, Format: Range)

Meaning: Range of indexes of q-points/transferred momenta to be computed.

Tip: Set to 1 1 to select just the long wavelength term.

BndsRnXd (Units: None, Format: Range)

Meaning: Range of bands included in the sum.

Tip: Range of bands incluein blah blah

EnRngeXd (Units: Energy, Format: Range)

Meaning: Energy range the spectrum is calculated across.

Tip: Energy range blah blah

DmRngeXd (Units: Energy, Format: Range)

Meaning: Determines the damping used across the requested spectral range.

Tip: Typically this is kept constant. If different values are used, the damping at each energy will be interpolated linearly. This can be useful when poor k-point sampling leads to large oscillations at higher energy.

ETStpsXd (Units: None, Format: Integer)

Meaning: Number of energy steps.

Tip: Determines the number of steps in energy the response function/spectrum is computed for in the desired range defined by EnRngeXd.

LongDrXd (Units: Length, Format: Vector)

Meaning: Electric field direction.

Tip: Electric field direction

Optics-advanced

FFTGvecs (Units: RL/Energy, Format: Integer/Real)

Meaning: Number of G-vectors or energy cut off for expanding the wavefunctions/FFT transforms

Tip: It needs careful convergence. Determines the memory needed.

DrudeWXd (Units: Energy, Format: Complex)

Meaning: Drude plasmon energy and inverse lifetime.

Tip: Drudes

Coulomb cutoff

CutRadius (Units: Length, Format: Real)

Meaning: Sphere/cylinder radius.

Tip: TIP

CUTBox (Units: Length, Format: Vector)

Meaning: Box sides.

Tip: BOX

CUTGeo (Units: None, Format: String)

Meaning: Cutoff geometry.

Tip: Allowed values are: "box/cylinder/sphere X/Y/Z/XY...", e.g. "box xy" or "cylinder y".

GW

EXXRLvcs (Units: RL/Energy, Format: Integer/Real)

Meaning: Number of G-vectors used in the sum of the exchange self-energy Sx.

Tip: It needs careful convergence: not particularly time consuming, large values can be used to ensure convergence.

QPkrange (Units: None , Format: Range )

Meaning: First and last Indexes of kpoints and bands the self energy correction is calculated

Tip: If interested in non consecutive kpoints or bands multiple rows can be also considered

BSK

BSENGexx (Units: RL/Energy, Format: Integer/Real)

Meaning: G-components to be summed in the Exchange part of the BSE kernel, which takes into account the Local-field effects

Tip: Small values increase speed. Convergence tests are required.

BSENGBlk (Units: RL/Energy, Format: Integer/Real)

Meaning: Number of RL-components of the Screened Coulomb Potential matrix W(G,G'), to be included in the sum of the e-h attractive Kernel

Tip: Try using the diagonal terms only first (BSresKmod BScplKmod variables); use a smaller number than the dimension of the Screened interaction matrix

Note: You can also add extra stuff, formulae, images etc below the template entry if the template is not able to handle it

BSEBands (Units: None, Format: Range)

Meaning: Bands range: Specifies the band states from which the electron-hole basis of the BSE kernel is constructed

Tip: Choose few bands close to the Fermi level.

KfnQP_E (Units: eV/None/None, Format: Scissors)

Meaning: QP corrections using a scissor operator and valence/conduction stretching.

Tip: From a previous GW calculation or experiment.