Isoscalar Monopole Strength in $^{100}$Mo: an Indicator for Static Triaxial Deformation in The Ground State


 % We perform deformation constraint symmetry-unrestricted 3D time-dependent density functional theory (TDDFT) calculations for the isoscalar monopole (ISM) mode in $^{100}$Mo. Monopole moments as a function of time are obtained by time propagating states based on different deformations. A Fourier transform is then performed on the obtained response functions. The resulted ISM strength functions are compared with experimental data. % For the static potential-energy-surface (PES) calculations, the results using SkM* and \UNEDFONE~energy-density functionals (EDFs) show spherical ground states and considerable softness in the triaxial deformation. The PES obtained with SLy4 EDF shows a static triaxial deformation. The TDDFT results based on different deformations show that a quadrupole deformation {\bf (characterized by $\beta_2$)} value of 0.25-0.30 give a two-peak structure of the strength functions. Increasing triaxial deformation {\bf (characterized by $\gamma$)} from 0$^{\circ}$ to 30$^{\circ}$ results in the occurrence of an additional peak between the two, making the general shape of the strength functions closer to the data. % Our microscopic TDDFT analyses suggest that the $^{100}$Mo is triaxially deformed in the ground state. The calculated isoscalar $Q_{20}$ and $Q_{22}$ strength functions show peaks at lower energies. The coupling of these two modes with the ISM mode is the reason for the three-peak/plateau structure in the strengths of $^{100}$Mo.