elambros / exchcxx

Exchange correlation (XC) library for density functional theory (DFT) calculations in modern C++

About

ExchCXX Copyright (c) 2020-2022, The Regents of the University of California, through Lawrence Berkeley National Laboratory (subject to receipt of any required approvals from the U.S. Dept. of Energy). All rights reserved.

If you have questions about your rights to use or distribute this software, please contact Berkeley Lab's Intellectual Property Office at [email protected].

NOTICE. This Software was developed under funding from the U.S. Department of Energy and the U.S. Government consequently retains certain rights. As such, the U.S. Government has been granted for itself and others acting on its behalf a paid-up, nonexclusive, irrevocable, worldwide license in the Software to reproduce, distribute copies to the public, prepare derivative works, and perform publicly and display publicly, and to permit others to do so.

Synopsis

ExchCXX is a modern C++ library for the evaluation of exchange-correlation (XC) functionals required for density functional theory (DFT) calculations. In addition to providing high-level wrappers for the ubiquitous Libxc library for the CPU evaluation of XC functionals, ExchCXX also provides locally developed implementations of a small subset of XC functionals which may be evaluated either on the host (CPU) or device (GPU, FPGA, etc). Currently GPU support is provided through the CUDA for NVIDIA GPUs, HIP for AMD GPUs and SYCL (experimental) for generic accelerator backends (including Intel GPUs).

ExchCXX is a work in progress. Its development has been funded by the U.S. Department of Energy Exascale Computing Project (NWChemEx).

Design Goals

• Provide a modern C++ wrapper around various XC functional libraries (Libxc, XCFun, etc)
• Provide stable, portable and high-performance implementations for the evaluation of XC functionals on various accelerator architectures (GPUs, FPGAs, etc)

Example Usage

// Setup the B3LYP Functional
using namespace ExchCXX;

auto backend = Backend::builtin; // Set to Backend::libxc for Libxc wrapper
auto func    = Functional::B3LYP;
auto polar   = Spin::Polarized; // Set to Unpolarized for unpolaried calculation

XCFunctional b3lyp( backend, func, polar );


// Evaluate on Host (CPU)
size_t npts = ...;
std::vector<double> 
  rho(b3lyp.rho_buffer_len(npts)), 
  sigma(b3lyp.sigma_buffer_len(npts)), 
  exc(b3lyp.exc_buffer_len(npts)), 
  vrho(b3lyp.vrho_buffer_len(npts)), 
  vsigma(b3lyp.vsigma_buffer_len(npts));

// Set up rho / gamma

b3lyp.eval_exc_vxc( npts, rho.data(), gamma.data(), exc.data(), vrho.data(),
  vgamma.data() );


// Evaluate on the Device (GPU)
cudaStream_t stream = ...;

double *rho_device, *gamma_device, *exc_device, *vrho_device, *vgamma_device;

// Allocate device memory
// Send rho / gamma to device

b3lyp.eval_exc_vxc_device( npts, rho_device, gamma_device, exc_device, vrho_device,
  vgamma_device, stream );

Implemented XC Functional Interfaces

XCKernel

Name	Libxc Identifier	ExchCXX Identifier	Device?
Slater Exchange	XC_LDA_X	Kernel::SlaterExchange	Y
Vosko-Wilk-Nusair III	XC_LDA_C_VWN_3	Kernel::VWN3	Y
Vosko-Wilk-Nusair V	XC_LDA_C_VWN_RPA	Kernel::VWN5	Y
Perdew-Burke-Ernzerhof (Exchange)	XC_GGA_X_PBE	Kernel::PBE_X	Y
Perdew-Burke-Ernzerhof (Correlation)	XC_GGA_C_PBE	Kernel::PBE_C	Y
Revised PBE from Zhang & Yang	XC_GGA_X_PBE_R	`Kernel::revPBE_X	Y
Perdew-Wang 91 (LDA)	XC_LDA_C_PW	Kernel::PW91_LDA	Y
Perdew-Wang 91 (LDA) Modified	XC_LDA_C_PW_MOD	Kernel::PW91_LDA_MOD	Y
Perdew-Wang 91 (LDA) RPA	XC_LDA_C_PW_RPA	Kernel::PW91_LDA_RPA	Y
Perdew-Zunger 86	XC_LDA_C_PZ	Kernel::PZ86_LDA	Y
Perdew-Zunger 86 Modified	XC_LDA_C_PZ_MOD	Kernel::PZ86_LDA_MOD	Y
Becke Exchange 88	XC_GGA_X_B88	Kernel::B88	Y
Lee-Yang-Parr	XC_GGA_C_LYP	Kernel::LYP	Y
PBE0	XC_HYB_GGA_XC_PBEH	Kernel::PBE0	Y
B3LYP	XC_HYB_GGA_XC_B3LYP	Kernel::B3LYP	Y

Feature Requests / Contributing

Although ExchCXX may in principle wrap any XC functional implemented by third-party software, generating these interfaces must currently be done by hand. As such, if there is a functional that you would like to see wrapped in either host or device code, please create a GitHub issue which details your request. Alternatively, we are more than happy to accept pull-requests if you have made the changes locally and would like to see them integrated in upstream.

License

ExchCXX is made freely available under the terms of a modified 3-Clause BSD license. See LICENSE.txt for details.

Acknowledgments

The development of ExchCXX is supported by the Exascale Computing Project (17-SC-20-SC), a collaborative effort of the U.S. Department of Energy Office of Science and the National Nuclear Security Administration.