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

Random Integration Method

RandQpts (Units: RL, Format: Integer)

Meaning: Number of random q-points in the BZ

Tip: It needs convergence: values like 10^6 can be used to ensure convergence.

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

LongDrXp (Units: Length, Format: Vector)

Meaning: Electric field direction in a plsmon pole calculation.

Tip: Pay attention how the system is oriented when treating non 3D systems and choose a direction in the plane/axis where your system lies

PPAPntXp (Units: Energy, Format: Real)

Meaning: Plasmon pole Imaginary Energy (Default 1 Ha)

Tip: The self energy in the imaginary axis should be a smooth function so it should not have a strong dependence on this pole energy. Set it at an higher value of the plasmon energy (see EELS spectrum)

BndsRnXp (Units: None, Format: Range)

Meaning: Bands range: Specifies the number of bands entering in the sum over states in the RPA response function in a plasmon pole calculation

Tip: It needs several empty states. See also GTermKind variable in order to speed up the convergences.

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

Meaning: Number of G-vectors or energy cut off in the screening in a plsmon pole calculation.

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.

GbndRnge (Units: None, Format: Range)

Meaning: Bands range: Specifies the number of bands entering in the sum over states in the correlation part of the self energy

Tip: It needs several empty states. Single quasiparticle states converges very slowly with respect GbndRnge, energy differences (e.g. gaps) behave better. See also GTermKind variable in order to speed up the convergences.

BSK & BSS

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 stretching coefficients for the conduction/valence bandwidths.

Tip: From a previous GW calculation or experiment.

KfnQP_E (Units: none, Format: string)

Meaning: From a previous GW calculation. An interpolation of the missing QP-values on the basis of the QP-database is available

Tip: {{{5}}}

KfnQP_E (Units: none, Format: integer)

Meaning: Interpolation neighbours

Tip:

BSHayTrs (Units: none, Format: real)

Meaning: Haydock treshold. Strict(>0)/Average(<0)

Tip: