  Spectroscopic calculations are carried out, for the description of the
shape/phase transition in Pt nuclei in terms of the Interacting Boson Model
(IBM) Hamiltonian derived from (constrained) Hartree-Fock-Bogoliubov (HFB)
calculations with the finite range and density dependent Gogny-D1S Energy
Density Functional. Assuming that the many-nucleon driven dynamics of nuclear
surface deformation can be simulated by effective bosonic degrees of freedom,
the Gogny-D1S potential energy surface (PES) with quadrupole degrees of freedom
is mapped onto the corresponding PES of the IBM. Using this mapping procedure,
the parameters of the IBM Hamiltonian, relevant to the low-lying quadrupole
collective states, are derived as functions of the number of valence nucleons.
Merits of both Gogny-HFB and IBM approaches are utilized so that the spectra
and the wave functions in the laboratory system are calculated precisely. The
experimental low-lying spectra of both ground-state and side-band levels are
well reproduced. From the systematics of the calculated spectra and the reduced
E2 transition probabilities $B$(E2), the prolate-to-oblate shape/phase
transition is shown to take place quite smoothly as a function of neutron
number $N$ in the considered Pt isotopic chain, for which the $\gamma$-softness
plays an essential role. All these spectroscopic observables behave
consistently with the relevant PESs and the derived parameters of the IBM
Hamiltonian as functions of $N$. Spectroscopic predictions are also made for
those nuclei which do not have enough experimental E2 data.
