Variables: Difference between revisions

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This page gives a brief explanation of the format and meaning for input variables used by Yambo.  
This page gives a brief explanation of the format and meaning for input variables used by Yambo. Check the [[Units]] and [[Formats]] pages for accepted values of each.
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Links can be made to runlevel sections with <nowiki>Variables#Initialization</nowiki> and to single variables with <nowiki>Variables#MaxGvecs</nowiki>, 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. -->
Links can be made to runlevel sections with <nowiki>Variables#Initialization</nowiki> and to single variables with <nowiki>Variables#MaxGvecs</nowiki>, 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. THIS CAN BE FIXED WITH NAMED OPTIONS -->
[[Units]]
[[Formats]]
===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.
<!--* Time = ps, fs, as
* Magnetic field = T
* Electric field = V/mm
* Angle = deg, rad -->
 
===Formats===
* Integer = integer value
* Real = real value
* Complex = <code>( real part , imag part )</code>
* String = string
* Range = <code>Lower limit | Upper limit |</code>(in the specified Unit or integer values)
* Scissors = <code>Shift | CB stretch | VB stretch |</code> (Energy | Real | Real)
* Logical = uncommented=.true.
* Vector = <code>x | y | z  |</code> (in Cartesian coordinates, sandwiched by %)
Ranges can also be split on multiple lines.


===Index===
===Index===

Revision as of 08:53, 12 September 2017

This page gives a brief explanation of the format and meaning for input variables used by Yambo. Check the Units and Formats pages for accepted values of each.

Index

MaxGvecs
Chimod | NGBlkXd | QpntsRXd

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 included in the calculation of X0

EnRngeXd (Units: Energy, Format: Range)
Meaning: Energy range the spectrum is calculated across.
Tip: Extremae of the energy range across which optical spectra will be computed.

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. In the case of a full frequency GW the range is fixed by the occupied/empty states included in the calculation, the number of frequency requires a careful check

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.

ExtendOut (Units: None, Format: Flag)
Meaning: Extended output: Print more quantities in qp output files
Tip: Optional variable (-V qp). Uncomment to activate

GTermKind (Units: None, Format: String)
Meaning: Type of terminator to accelarate onvergence with respect empty states
Tip: Default is "none", possible options are "BG" for the Bruneval-Gonze terminator.
See BG[1].


GfnQPdb (Units: none, Format: string)
Meaning: Database for QP corrections.
Tip: From a previous GW calculation. An interpolation of the missing QP-values on the basis of the QP-database is available. To be used for a GW self consistent calcuation.
Format: "<what> < <path>/ndb.QP" with <what> = E,W,Z for QP energy correction, QP width and renormalization factor

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.

KfnQPdb (Units: none, Format: string)
Meaning: Database for QP corrections.
Tip: From a previous GW calculation. An interpolation of the missing QP-values on the basis of the QP-database is available
Format: "<what> < <path>/ndb.QP" with <what> = E,W,Z for QP energy correction, QP width and renormalization factor.

KfnQP_E (Units: none, Format: integer)
Meaning: Interpolation neighbours
Tip: (etc)

BSHayTrs (Units: none, Format: real)
Meaning: Haydock treshold. Strict(>0)/Average(<0)
Tip: (etc)


References

  1. ↑ F. Bruneval and X. Gonze, Physical Review B 78, 085125 (2008 )
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