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P. Gunacker, M. Wallerberger, E. Gull, A. Hausoel, G. Sangiovanni, K. Held:
"Continuous-time quantum Monte Carlo using worm sampling";
Physical Review B, 92 (2015), S. 155102-1 - 155102-10.

We present a worm sampling method for calculating one- and two-particle Green´s functions using continuous-
time quantum Monte Carlo simulations in the hybridization expansion (CT-HYB). Instead of measuring Green´s
functions by removing hybridization lines from partition function configurations, as in conventional CT-HYB, the
worm algorithm directly samples the Green´s function. We show that worm sampling is necessary to obtain general
two-particle Green´s functions which are not of density-density type and that it improves the sampling efficiency
when approaching the atomic limit. Such two-particle Green´s functions are needed to compute off-diagonal
elements of susceptibilities and occur in diagrammatic extensions of the dynamical mean-field theory and in
efficient estimators for the single-particle self-energy.

http://dx.doi.org/10.1103/PhysRevB.92.155102