Yambo is a computer

software Software is a set of computer programs and associated software documentation, documentation and data (computing), data. This is in contrast to Computer hardware, hardware, from which the system is built and which actually performs the work. ...

package for studying

many-body theory The many-body problem is a general name for a vast category of physical problems pertaining to the properties of microscopic systems made of many interacting particles. ''Microscopic'' here implies that quantum mechanics has to be used to provid ...

aspects of

solid Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural ...

s and

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...

systems. It calculates the excited state properties of physical systems from

first principle In philosophy and science, a first principle is a basic proposition or assumption that cannot be deduced from any other proposition or assumption. First principles in philosophy are from First Cause attitudes and taught by Aristotelians, and nua ...

s, e.g., from

quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistr ...

law without the use of empirical data. It is an

open-source software Open-source software (OSS) is computer software that is released under a license in which the copyright holder grants users the rights to use, study, change, and distribute the software and its source code to anyone and for any purpose. Op ...

released under the

GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general ...

(GPL). However the main development repository is private and only a subset of the features available in the private repository are cloned into the public repository and thus distributed.

Excited state properties

Yambo can calculate: *

Quasiparticle In physics, quasiparticles and collective excitations are closely related emergent phenomena arising when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in vacuum. For exa ...

energies: plasmon pole, COHSEX approximation, or real-axis *Lifetimes within the

GW approximation The ''GW'' approximation (GWA) 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's function ...

Optical absorption In physics, absorption of electromagnetic radiation is how matter (typically electrons bound in atoms) takes up a photon's energy — and so transforms electromagnetic energy into internal energy of the absorber (for example, thermal energy). ...

: RPA, Bethe Salpeter with or without Tamm-Dancoff approximation, TDDFT in TD-LDA or LRC *

Electron energy loss spectroscopy In electron energy loss spectroscopy (EELS) 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 pa ...

*Dynamical polarizability *electron-phonon coupling (static and dynamic perturbation theory) *magneto optical properties *surface spectroscopy

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,

nanowire A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre (10−9 metres). More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less ...

polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

chains). It can also handle collinear (i.e., spin-polarized

wave function A wave function in quantum physics is a mathematical description of the quantum state of an isolated quantum system. The wave function is a complex-valued probability amplitude, and the probabilities for the possible results of measurements ...

s) and non-collinear (

spinor In geometry and physics, spinors are elements of a complex vector space that can be associated with Euclidean space. Like geometric vectors and more general tensors, spinors transform linearly when the Euclidean space is subjected to a sligh ...

s) magnetic systems. Typical systems are of the size of 10-100 atoms, or 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 theory Time-dependent density-functional theory (TDDFT) 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 magne ...

. Quasiparticle energies are calculated within the

for the self energy. Optical properties are calculated either by solving the

Bethe–Salpeter equation The Bethe–Salpeter equation (named after Hans Bethe and Edwin Salpeter) describes the bound states of a two-body (particles) quantum field theoretical system in a relativistically covariant formalism. The equation was actually first published i ...

or by using the adiabatic local density approximation within time-dependent density functional theory.

Numerical details

Yambo uses a

plane wave In physics, a plane wave is a special case of wave or field: a physical quantity whose value, at any moment, is constant through any plane that is perpendicular to a fixed direction in space. For any position \vec x in space and any time t, ...

s basis set to represent the electronic (single-particle) wavefunctions. Core electrons are described with norm-conserving

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. The pseudopotential approximation was first introduced ...

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:

ABINIT ABINIT 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 ...

, PWscf, CPMD 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 Fortran 95 and C *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 analysis and visualization of the results.

System requirements, portability

Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...

based systems *

Compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs tha ...

s for the programming languages Fortran 95 and C *optional: PGI Fortran compiler for

GPU A graphics processing unit (GPU) is a specialized electronic circuit designed to manipulate and alter memory to accelerate the creation of images in a frame buffer intended for output to a display device. GPUs are used in embedded systems, mobi ...

version (starting from 4.5 release) *optional
netcdffftwmpi
(for parallel execution)
etsf-iolibxchdf5
*Hardware requirements depend very much on the physical system under study and the chosen level of theory. For

random-access memory Random-access memory (RAM; ) is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written in almost the ...

(RAM) the requirements may vary from less than 1 GB to few GBs, depending on the problem.

Learning Yambo

The Yambo team provides
wiki
web-page with a list o
tutorials
an
lecture notes
On the yambo web-site there is also a list of al
thesis
done with the code.

Non-distributed part

Part of the YAMBO code is kept under a private repository. These are the features implemented and not yet distributed: *total energy using adiabatic-connection fluctuation-dissipation theorem *magnetic field *self-consistent GW *dynamical Bethe–Salpeter *finite-momentum Bethe-Salpeter *real-time spectroscopy *advanced kernels for time-dependent density functional theory (Nanoquanta kernel).

References

External links

* * {{DEFAULTSORT:Yambo Code Physics software Computational chemistry software Free physics software