YAMBO code
Encyclopedia
Yambo is an open source Many-body theory
software package for study solids and molecular systems. It calculates the excited state properties of physical systems from first principles (e.g. from quantum mechanics law without the use of empirical data).
two dimensions (surfaces) and one dimension (e.g. nanotubes, nanowires, polymeric chains)
Typical systems are of the size of 10-100 atoms/10-400 electrons (per unit cell in the case of periodic systems).
. In particular quasiparticle energies are calculated within the GW approximation
for the self energy. Optical
properties are calculated either by solving the Bethe-Salpeter equation
or by using the adiabatic local density approximation within
time-dependent density functional theory.
s basis set to represent the electronic
(single-particle) wavefunctions. Core electrons are described with
norm-conserving pseudopotential
s.
The choice of a plane-wave basis set enforces the periodicity of the
systems. Isolated systems, and systems that are periodic in only one
or two directions can be treated by using a supercell approach.
For such systems Yambo offers two numerical techniques for the
treatment of the Coulomb integrals: the cut-off and the
random-integration method.
Many-body theory
The many-body theory is an area of physics which provides the framework for understanding the collective behavior of vast assemblies of interacting particles. In general terms, the many-body theory deals with effects that manifest themselves only in systems containing large numbers of constituents...
software package for study solids and molecular systems. It calculates the excited state properties of physical systems from first principles (e.g. from quantum mechanics law without the use of empirical data).
Excited state properties
With Yambo one can calculate:- QuasiparticleQuasiparticleIn physics, quasiparticles are emergent phenomena that occur when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in free space...
energies (plasmon pole, COHSEX approximation or real-axis ) - Lifetimes within the GW approximationGW approximationThe GW approximation is an approximation made in order to calculate the self-energy of a many-body system of electrons. The approximation is that the expansion of the self-energy Σ in terms of the single particle Green function G and the screened Coulomb interaction W can be truncated after the...
- Optical absorption (RPA, Bethe Salpeter with or without Tamm-Dancoff Approximation, TDDFT in TD-LDA or LRC)
- Electron energy loss spectroscopyElectron energy loss spectroscopyIn electron energy loss spectroscopy a material is exposed to a beam of electrons with a known, narrow range of kinetic energies. Some of the electrons will undergo inelastic scattering, which means that they lose energy and have their paths slightly and randomly deflected...
- Dynamical polarizability
Physical systems
Yambo can treat molecules and periodic systems (both metallic an insulating) in three dimensions (crystalline solids)two dimensions (surfaces) and one dimension (e.g. nanotubes, nanowires, polymeric chains)
Typical systems are of the size of 10-100 atoms/10-400 electrons (per unit cell in the case of periodic systems).
Theoretical methods and approximations
Yambo relies on many-body perturbation theory and time-dependent density functional theoryTime-dependent density functional theory
Time-dependent density functional theory is a quantum mechanical theory used in physics and chemistry to investigate the properties and dynamics of many-body systems in the presence of time-dependent potentials, such as electric or magnetic fields...
. In particular quasiparticle energies are calculated within the GW approximation
GW approximation
The GW approximation is an approximation made in order to calculate the self-energy of a many-body system of electrons. The approximation is that the expansion of the self-energy Σ in terms of the single particle Green function G and the screened Coulomb interaction W can be truncated after the...
for the self energy. Optical
properties are calculated either by solving the Bethe-Salpeter equation
Bethe-Salpeter equation
The Bethe–Salpeter equation, named after Hans Bethe and Edwin Salpeter, describes the bound states of a two-body quantum field theoretical system in a relativistically covariant formalism...
or by using the adiabatic local density approximation within
time-dependent density functional theory.
Numerical details
Yambo uses a plane wavePlane wave
In the physics of wave propagation, a plane wave is a constant-frequency wave whose wavefronts are infinite parallel planes of constant peak-to-peak amplitude normal to the phase velocity vector....
s basis set to represent the electronic
(single-particle) wavefunctions. Core electrons are described with
norm-conserving pseudopotential
Pseudopotential
In physics, a pseudopotential or effective potential is used as an approximation for the simplified description of complex systems. Applications include atomic physics and neutron scattering.- Atomic physics :...
s.
The choice of a plane-wave basis set enforces the periodicity of the
systems. Isolated systems, and systems that are periodic in only one
or two directions can be treated by using a supercell approach.
For such systems Yambo offers two numerical techniques for the
treatment of the Coulomb integrals: the cut-off and the
random-integration method.
Technical details
- Yambo is interfaced with plane-wave density-functional codes: ABINITABINITABINIT is an open-source suite of programs for materials science, distributed under the GNU General Public License. ABINIT implements density functional theory, using a plane wave basis set and pseudopotentials, to compute the electronic density and derived properties of materials ranging from...
, PWscfPWscfPWscf is a set of programs for electronic structure calculations within density functional theory and density functional perturbation theory, using plane wave basis sets and pseudopotentials. The software is released under the GNU General Public License....
, CPMDCPMDThe Car–Parrinello Molecular Dynamics,, also known as CPMD, is a method to follow the classical motion of point-like atomic nuclei in time, i.e. for performing molecular dynamics , while at the same time solving ab-initio and efficiently the quantum mechanical motion of electrons...
and with the ETSF-io library. The utilities that interface these codes with Yambo are distributed along with the main program. - The source code is written in C/Fortran95
- The code is parallelized using MPI running libraries
User interface
- Yambo has a command line user interface. Invoking the program with specific option generates the input with default values for the parameters consistent with the present data on the system.
- A postprocessing tool, distributed along with the main program, helps with the analisys and visualization of the results.
System requirements/portability
- Unix based systems
- c and fortran 95 compilers
- optional: netcdf,fftw, mpi (for parallel execution), etsf-io, libxc, hdf5
- Hardware requirements depends very much on the physical system under study and the chosen level of theory. For the RAM the requirements may vary from less than 1GB to few GBs depending on the problem.
Non-GPL part
Part of the YAMBO code is not released in the GPL version, these are the features implemented in the non-GPL part:- total energy using adiabatic-connection fluctuation-dissipation theorem
- electron-phonon coupling (static and dynamic perturbation theory)
- spin polarized systems
- magnetic field
- surface spectroscopy
- self-consistent GW
- dynamical Bethe-Salpeter
- advanced kernels for time-dependent density functional theory (Nanoquanta kernel).
External links
- yambo-code.org
- Yambo repository
- Yambo Tutorials
- Yambo Lecture Notes
- Yambo project is supported by the European Theoretical Spectroscopy Facility.