Monte Carlo simulation of spin-aligned atomic hydrogen

The density dependent ground-state properties of spin-aligned atomic hydrogen are studied using the Monte Carlo technique for 32 and 128 atoms in a cube with periodic boundary conditions. The one-particle density matrix, the two-body correlation function, the structure and pairing function have been evaluated and are compared to other recent work. The total number of particles in the condensate is largest at a density 6·10^–3 Å^–3 and amounts to ⁰=2.03·10^–3Å^–3. In addition, the elementary excitation spectrum is discussed in the framework of the Brueckner-Sawada theory. The correct initial slope of the spectrum is obtained from variational results on the structure function. From these results one may tentatively conclude that the roton like part of the spectrum disappears at densities less than 10^–2 Å^–3.