triqs_ctseg::measure_gt

#include <triqs_ctseg.hpp>

class measure_gt

Measure for the Green’s function in imaginary time

The imaginary-time Green’s function is defined as

\[G^\sigma_{ab}(\tau) = -\langle T_\tau c_{a\sigma}(\tau)c_{b\sigma}^\dagger(0) \rangle\]

and the corresponding improved estimator is given by

\[F_{ab}^{\sigma}(\tau) = -\int_0^\beta d\tilde{\tau} \sum_{c\sigma'} \langle T_\tau n_{c\sigma'}(\tilde{\tau}) \mathcal{U}^{\sigma\sigma'}_{ac}(\tilde{\tau}-\tau) c_{a\sigma}(\tau)c_{b\sigma'}^\dagger(0) \rangle\]

The imaginary-time measurement is most efficient. The performance of the

algorithm does not scale with the number of points in the grid on which it is measured, so this number can and should be chosen large. By Nyquist’s theorem, the Fourier transform will be correctly reproduce the function in the frequency domain on the first \(N_\omega\approx N_\tau/4\pi\) frequencies.

These measurements are turned on by setting measure_gt and measure_ft

to true, respectively. *The number of time points on the grid is specified through n_tau and is the same for both observables.

Public members

params	const triqs_ctseg::qmc_parameters *
config	const triqs_ctseg::configuration *
gt	block_gf<triqs::gfs::imtime> &
ft	block_gf<triqs::gfs::imtime> &
fprefactor	std::shared_ptr<precompute_fprefactor>
beta	double
Noverbeta	double
Z	double
gt_stack	observable<double>
Z_stack	observable<double>
counter	int
accum	double

Member functions

(constructor)
accumulate
collect_results